Inorganically filled, starch-bound compositions for manufacturing containers and other articles having a thermodynamically controlled cellular matrix

ABSTRACT

Compositions, methods, and systems for manufacturing articles, particularly containers and packaging materials, having a particle packed, highly inorganically filled, cellular matrix are disclosed. Suitable inorganically filled mixtures are prepared by mixing together a starch-based binder, a solvent, inorganic aggregates, and optimal admixtures, e.g., fibers, mold-releasing agents, rheology-modifying agents, plasticizers, coating materials, and dispersants, in the correct proportions to form an article which has the desired performance criteria. The inorganically filled mixtures have a predetermined viscosity and are heated between molds at an elevated temperature and pressure to produce form-stable articles having a desired shape and a selectively controlled cellular, structure matrix. The molded articles may be placed in a high humidity chamber to obtain the necessary flexibility for their intended use. The articles may be manufactured to have properties substantially similar to articles presently made from conventional materials like paper, paperboard, polystyrene, plastic, or other organic materials. They have especial utility in the mass-production of containers, particularly food and beverage containers.

This application is a continuation-in-part of U.S. Ser. No. 08/218,971filed Mar. 25, 1994 (pending), which is a continuation-in-part of Ser.No. 07/929,898 filed Aug. 11, 1992, now abandoned. This application isalso a continuation-in-part of U.S. Ser. No. 08/109,100 filed Aug. 18,1993, now abandoned, which is a continuation-in-part of Ser. No.07/929,898 filed Aug. 11, 1992, now abandoned. This application is alsoa continuation-in-part of U.S. Ser. No. 08/095,662 filed Jul. 21, 1993,now U.S. Pat. No. 5,385,764, which is a continuation-in-part of Ser. No.07/929,898 filed Aug. 11, 1992, now abandoned. This application is alsoa continuation-in-part of U.S. Ser. No. 07/982,383 filed Nov. 25, 1992,now abandoned, which is a continuation-in-part of Ser. No. 07/929,898filed Aug. 11, 1992, now abandoned. This application is also acontinuation-in-part of U.S. Ser. No. 08/288,667 filed Aug. 9, 1994(pending).

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to compositions formanufacturing cellular articles from highly inorganically filledmaterials having a starch-based binder. More particularly, the presentinvention relates to economically mass-produced, environmentallysuperior containers and other articles prepared by combining particlepacked inorganic fillers and a starch-based binder with a solvent andother desired admixtures to form a mixture having a controlledviscosity. The mixture is positioned between opposing molds where thetemperature and pressure are elevated to rapidly form the mixture into aform-stable article having a selectively designed cellular structuralmatrix. The components for the mixture and the processing parameters canbe selected to produce articles that have desired properties of, e.g.,thickness, stiffness, flexibility, insulation, toughness, productstability, and strength. The resulting articles can also be producedless expensively and more environmentally safe than articles made fromconventional materials, e.g., paper, plastic, polystyrene foam, glass,or metal.

2. Relevant Technology

A. Articles of Manufacture

Materials such as paper, paperboard, plastic, polystyrene, and evenmetals are presently used in enormous quantity in the manufacture ofarticles such as containers, separators, dividers, lids, tops, cans, andother packaging materials. Advanced processing and packaging techniquespresently allow an enormous variety of liquid and solid goods to bestored, packaged, or shipped in such packaging materials while beingprotected from harmful elements.

Containers and other packaging materials protect goods fromenvironmental influences and distribution damage, particularly fromchemical and physical influences. Packaging helps protect an enormousvariety of goods from gases, moisture, light, microorganisms, vermin,physical shock, crushing forces, vibration, leaking, or spilling. Somepackaging materials also provide a medium for the dissemination ofinformation to the consumer, such as the origin of manufacture,contents, advertising, instructions, brand identification, and pricing.

Typically, most containers and other packaging materials (includingdisposable containers) are made from paper, paperboard, plastic,polystyrene, glass, or metal materials. Each year, over 100 billionaluminum cans, billions of glass bottles, and thousands of tons of paperand plastic are used in storing and dispensing soft drinks, juices,processed foods, grains, beer, and other products. Outside of the foodand beverage industry, packaging containers (and especially disposablecontainers) made from such materials are ubiquitous. Paper-basedarticles made primarily from tree derived wood pulp are alsomanufactured each year in enormous quantities. In the United Statesalone, approximately 5.5 million tons of paper are consumed each yearfor packaging purposes, which represents only about 15% of the totalannual domestic paper production.

B. The Impact of Paper, Plastic, Glass and Metal

Recently, there has been a debate as to which of the conventionalmaterials (e.g., paper, paperboard, plastic, polystyrene, glass, ormetal) is most damaging to the environment. Consciousness-raisingorganizations have convinced many people to substitute one material foranother in order to be more environmentally "correct." The debate oftenmisses the point that each of these materials has its own uniqueenvironmental weaknesses. One material may appear superior to anotherwhen viewed in light of a particular environmental problem, whileignoring different, often larger, problems associated with thesupposedly preferred material.

Polystyrene products, particularly containers and other packagingmaterials, have more recently attracted the ire of environmental groups.While polystyrene itself is a relatively inert substance, itsmanufacture involves the use of a variety of hazardous chemicals andstarting materials. Unpolymerized styrene is very reactive, andtherefore presents a health problem to those who must handle it. Becausestyrene is manufactured from benzene (a known mutagen and a probablecarcinogen), residual quantities of benzene can be found in styrene.

More potentially damaging has been the use of chlorofluorocarbons (or"CFCs") in the manufacture of "blown" or "expanded" polystyreneproducts. This is because CFCs have been linked to the destruction ofthe ozone layer. In the manufacture of foams, including blownpolystyrene, CFCs (which are highly volatile liquids) have been used to"expand" or "blow" the polystyrene into a foamed material, which is thenmolded into the form of cups, plates, trays, boxes, "clam-shell"containers, spacers, or packaging materials. Even the substitution ofless "environmentally damaging" blowing agents (e.g., HCFCs, pentanes,and CO₂ with hydrocarbon combinations) are still significantly harmfuland their elimination would be beneficial.

As a result, there has been widespread pressure for companies to stopusing polystyrene products in favor of more environmentally safematerials. Some environmental groups have favored a temporary return tothe use of more "natural" products, such as paper or other products madefrom wood pulp, which are believed to be biodegradable. Nevertheless,other environmental groups have taken the opposite view in order tominimize the cutting of trees and depletion of forests.

Although paper products are ostensibly biodegradable and have not beenlinked to the destruction of the ozone layer, recent studies have shownthat the manufacture of paper probably more strongly impacts theenvironment than does the manufacture of polystyrene. In fact, the woodpulp and paper industry has been identified as one of the five toppolluters in the United States. For instance, products made from paperrequire ten times as much steam, fourteen to twenty times theelectricity, and twice as much cooling water as compared to anequivalent polystyrene product. Various studies have shown that theeffluent from paper manufacturing contains ten to one hundred times theamount of contaminants produced in the manufacture of polystyrene foam.

In addition, a by-product of paper manufacturing is that the environmentis impacted by dioxin, a harmful toxin. Dioxin, or more accurately,2,3,7,8-tetrachlorodibenzo[b,e][1,4]-dioxin, is a highly toxiccontaminant, and is extremely dangerous, even in very low quantities.Toxic effects of dioxin in animals and humans include anorexia, severeweight loss, hepatoxicity, hematoporphyrin, vascular lesions, chloracne,gastric ulcers, porphyrinuria, porphyria, cutanea tarda, and prematuredeath. Most experts in the field believe that dioxin is a carcinogen.

Another drawback of the manufacture of paper and paperboard is therelatively large amount of energy that is required to produce paper.This includes the energy required to process wood pulp to the point thatthe fibers are sufficiently delignified and frayed that they areessentially self-binding under the principles of web physics. Inaddition, a large amount of energy is required in order to remove thewater within conventional paper slurries, which contain water in anamount of up to about 99.5% by volume. Because so much water must beremoved from paper slurries, it is necessary to literally suck water outof the slurry even before the drying process is begun. Moreover, much ofthe water that is sucked out during the dewatering processes is usuallydiscarded into the environment.

The manufacturing processes of forming metal sheets into containers(particularly cans made of aluminum and tin), blowing glass bottles, andshaping ceramic containers utilize high amounts of energy because of thenecessity to melt and then separately work and shape the raw metal intoan intermediate or final product. These high energy and processingrequirements not only utilize valuable energy resources, but they alsoresult in significant air, water, and heat pollution to the environment.While glass can be recycled, that portion that ends up in landfills isessentially non-degradable. Broken glass shards are very dangerous andcan persist for years.

Some of these pollution problems are being addressed; however, theresult is the use of more energy, as well as the significant addition tothe capital requirements for the manufacturing facilities. Further,while significant efforts have been expended in recycling programs, onlya portion of the raw material needs come from recycling--most of the rawmaterials still come from nonrenewable resources.

Even paper or paperboard, believed by many to be biodegradable, canpersist for years, even decades, within landfills where they areshielded from air, light, and water--all of which are required fornormal biodegradation activities. There are reports of telephone booksand newspapers having been lifted from garbage dumps that had beenburied for decades. This longevity of paper is further complicated sinceit is common to treat, coat, or impregnate paper with various protectivematerials that further slow or prevent degradation.

Another problem with paper, paperboard, polystyrene, and plastic is thateach of these requires relatively expensive organic starting materials,some of which are nonrenewable, such as the use of petroleum in themanufacture of polystyrene and plastic. Although trees used in makingpaper and paperboard are renewable in the strict sense of the word,their large land requirements and rapid depletion in certain areas ofthe world undermines this notion. Hence, the use of huge amounts ofessentially nonrenewable starting materials in making articles therefromcannot be sustained and is unwise from a long term perspective.Furthermore, the processes used to make the packaging stock rawmaterials (such as paper pulp, styrene, or metal sheets) are very energyintensive, cause major amounts of water and air pollution, and requiresignificant capital requirements.

In light of the foregoing, the debate should not be directed to which ofthese materials is more or less harmful to the environment, but rathertoward asking: Can we discover or develop an alternative material whichwill solve most, if not all, of the various environmental problemsassociated with each of these presently used materials?

C. Alternative Materials

Due to the more recent awareness of the tremendous environmental impactsof using paper, paperboard, plastic, polystyrene, and metals for avariety of single-use, mainly disposable, articles such as containersand other packaging materials made therefrom (not to mention the evermounting political pressures), there has been an acute need (long sincerecognized by those skilled in the art) to find environmentally soundsubstitute materials.

One alternative has been to make the desired articles and containers outof baked, edible sheets, e.g., waffles or pancakes. Although ediblesheets can be made into trays, cones, and cups which are easilydecomposed, they pose a number of limitations. Edible sheets areprimarily made from a mixture of water, flour, and a rising agent. Themixture is baked between heated molds into its desired shape. Fats oroils are added to the mixture to permit removal of the sheet from thebaking mold. Oxidation of these fats cause the edible sheets to gorancid. From a mechanical standpoint, the resulting edible sheets arevery brittle and far too fragile to replace most articles made fromconventional materials. Furthermore, edible sheets are overly sensitiveto moisture and can easily mold or decompose prior to or during theirintended use.

Attempts have also been made to make articles using organic binders. Forexample, articles have been made from mixtures of starch, water, and amold-releasing agent. The starch-based mixtures were baked betweenheated molds until the starch gelated and set in the desired shape forthe articles. The resulting products, however, were found to be costprohibitive. Slow processing times, expensive equipment, and therelatively high cost of starch compared to conventional materials madethe articles more expensive than conventional articles. Althoughinorganic fillers have been added to starch-based mixtures in an attemptto cut material cost, mixtures containing any significant portion offillers were unable to produce structurally stable articles that hadfunctional mechanical properties.

Furthermore, the starch-based articles were found to be very fragile andbrittle, giving them limited use. To improve flexibility, the articleswere placed in a humidity chamber where the moisture was absorbed by thestarch to soften the articles. The moisture absorption, however, tookseveral minutes, significantly slowing down the manufacturing process.Furthermore, an additional time-consuming step of applying a coating tothe article was required to prevent the moisture from escaping from thearticle once the article was finished. Attempts at producingorganic-based articles have also failed to consistently produce articlesthat have a smooth, uniform surface. To disguise the surface defects,the articles have usually been made with a waffled surface.

Industry has repeatedly sought to develop inorganically filled materialsfor the production of disposable articles that are mass-produced andused in large quantities. Inorganic materials such as clay, naturalminerals, and stone are easily accessed, nondepletable, inexpensive, andenvironmentally inert. In spite of economic and environmental pressures,extensive research, and the associated long-felt need, the technologysimply has not existed for the economic and feasible production ofhighly inorganically filled materials which could be substituted forpaper, paperboard, plastic, polystyrene, metal, or other organic-basedcontainers and other articles.

Significant attempts have been made over many years to fill conventionalpaper with inorganic materials, such as kaolin and/or calcium carbonate,although there is a limit (about 20-35% by volume) to the amount ofinorganics that can be incorporated into paper products. In addition,there have been attempts to fill certain plastic packaging materialswith clay in order to increase the breathability of the product andimprove the ability of the packaging material to keep fruits orvegetables stored therein fresh. In addition, inorganic materials areroutinely added to adhesives and coatings in order to impart certainproperties of color or texture to the final product. Nevertheless,inorganic materials only comprise a small fraction of the overallmaterial used to make packaging materials or other articles, rather thanmaking up the majority of the material mass. Attempts to increase theamount of inorganic filler in a polymer matrix have had significantadverse affects on the rheology and properties of the binding system,e.g., loss of strength, increased brittleness, etc..

In light of the fact that inorganic materials are typically the mosteconomical and ecological material, what is needed are highlyinorganically filled materials that can replace paper, paperboard,plastic, polystyrene, or metal materials as the material of choice forproducing containers and articles currently made therefrom. What isfurther needed is an inexpensive, environmentally safe, organic materialthat, in relatively small quantities, acts as a satisfactory binder forthe inorganic material.

It would be a further improvement in the art to form the highlyinorganically filled mixture having an organic binder into containersand other articles currently made from paper, paperboard, polystyrene,metal, plastic, or other organic materials.

It would be a significant improvement in the art if such mixturesyielded highly inorganically filled articles which had propertiessimilar to or superior to paper, paperboard, polystyrene, plastic, ormetal materials.

It would yet be an improvement in the art if the above containers andarticles could be manufactured with or without being placed in ahumidity chamber to obtain the desired flexibility.

It would be still another advantage in the art if the above articlescould be formed without the need to subsequently apply a coatingthereto.

It would be a an improvement in the art if the above articles andcontainers could be formed having a smoother, more uniform surface withfewer defects.

It would also be a tremendous improvement in the art if such articlescould be formed using existing manufacturing equipment and techniquespresently used to form such articles from paper, paperboard,polystyrene, plastic, or other organic materials.

It would be another improvement in the art if such compositions formanufacturing articles did not result in the generation of wastesinvolved in the manufacture of paper, paperboard, plastic, polystyrene,or metal materials.

It would be yet an advancement in the art if the compositions containedless water which had to be removed during the manufacturing process (ascompared to paper manufacturing) in order to shorten the processing timeand reduce the initial equipment capital investment.

In addition, it would be a significant improvement in the art if sucharticles were readily degradable into substances which are commonlyfound in the earth.

From a practical point of view, it would be a significant improvement ifsuch materials made possible the manufacture of containers and otherarticles at a cost that was comparable or even superior to existingmethods of manufacturing containers or other articles from paper,paperboard, plastic, polystyrene, or metal. Specifically, it would bedesirable to reduce the energy requirements, conserve valuable naturalresources, and reduce the initial capital investment for making articleshaving the desirable characteristics of conventional materials such aspaper, metals, polystyrene, plastic, or other organic materials.

From a manufacturing perspective, it would be a significant advancementin the art of shaping highly inorganically filled materials to providecompositions for mass-producing highly inorganically filled articleswhich could rapidly be formed and ready for use within a matter ofminutes from the beginning of the manufacturing process.

It would also be a tremendous advancement in the an to providecompositions which allow for the production of highly inorganicallyfilled materials having greater flexibility, flexural strength,toughness, moldability, mass-producibility, product stability, and lowerenvironmental impact compared to conventional materials having a highcontent of inorganic filler.

Such compositions and articles are disclosed and claimed herein.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention discloses novel compositions and articles ofmanufacture prepared from particle packed, highly inorganically filledmaterials having a starch-based binder and a thermodynamicallycontrolled cellular matrix. Initially, a materials science andmicrostructural engineering approach is used to develop an appropriateinorganically filled mixture. The components of the mixture and theiramounts are selected based on an understanding of the interrelationshipsbetween processing parameters and the properties of the individualcomponents, moldable mixture, and final article.

The mixture is designed to produce a final product having the desiredproperties for its intended use at minimal cost. Properties that can beoptimized include thickness, density, modulus of elasticity, compressivestrength, tensile strength, flexural strength, flexibility, range ofstrain, thermal capabilities, and specific heat. Because of the abilityto impart or alter these properties as needed, a wide variety ofarticles can be made, including cups, trays, cartons, boxes, bottles,crates, and numerous other articles used for, e.g., packaging, storing,shipping, serving, portioning, and dispensing.

The inventive mixtures can include a variety of environmentally safecomponents, including a starch-based binder, water, inorganicaggregates, inert organic aggregates, mold-releasing agents, fibers,rheology-modifying agents, cross-linkers, dispersants, plasticizers, andcoatings. The mixture is designed with the primary considerations ofmaximizing the inorganic components, minimizing the starch component andsolvent, and selectively modifying the viscosity to produce articlesquickly, inexpensively, and having the desired properties for theirintended use. The starch-based binder acts as the binding agent andtypically includes a starch such as potato starch, corn starch, waxycorn starch, rice starch, wheat starch, their grain predecessors, e.g.,flour and cracked grains, or their modified counterparts. A solvent,typically water, alcohol, or a combination thereof, is used to dispersethe components within the mixture and act as an agent for the gelationof the starch-based binder. In addition, the solvent, along with otheradmixtures such as rheology-modifying agents, plasticizers, anddispersants, help to create a mixture having the desired rheological, orflow, properties.

The starch-based binder may be added in its ungelated, granular form, orit may be pregelated. As the starch-based binder is heated, the granulesrupture, thereby allowing the long, single chain, amylose polymerslocated within the granules to stretch out and intertwine with otherstarch polymers, such as the highly branched amylopectin polymers. Thisprocess is referred to as gelation. Once the solvent is removed, theresulting interconnected mesh of starch polymers produces a solidmaterial. However, the relatively high cost of starch-based binder andthe excess time and energy necessary to remove the solvent make itimpractical to make articles solely out of starch.

To decrease the cost and also to impart desirable properties to thefinal article, inorganic fillers or aggregates are usually added to themixture in an amount greater than about 20% and even up to as high asabout 90% by weight of the total solids in the mixture. While this rangeapplies to most aggregates of relatively high density (greater thanabout 1 g/cm³), in the case of lower density, or "lightweight",aggregates (having a density less than about 1 g/cm³), such as expandedperlite or hollow glass spheres, the minimum weight will be less and isdependent upon the density of the particular aggregate in question. As aresult, it is more appropriate to express the concentration oflightweight aggregates in terms of volume percent, which will preferablybe included in a broad range from about 5% to about 85% by volume.

To obtain mixtures having a high concentration of inorganics, theinorganic aggregate particles are selected to have a shape and particlesize distribution that preferably produces a high packing density. Thisprocess is referred to as particle packing. It is further preferred thatthe particles have a relatively small specific surface area. Usingfillers with a high packing density and low specific surface areaminimizes the amount of starch-based binder and solvent needed in themixture. By minimizing the starch-based binder and solvent, the materialcosts and processing time to produce the article are minimized.Furthermore, by selecting aggregates having specific mechanical andphysical properties, those properties can be imparted into the finalarticles. For example, the aggregate can help control the specific heat,density, strength, and texture of the final article. One preferredinorganic aggregate is calcium carbonate.

Rheology-modifying agents, such as cellulose-based,polysaccharide-based, protein-based, and synthetic organic materials canbe added to control the viscosity and yield stress of the mixture.Increasing the viscosity helps to prevent settling or separation withinthe mixture and aids in the formation of the cellular, structuralmatrix. In general, mixtures that have a high viscosity producerelatively dense articles having small cells in the structural matrix.In contrast, mixtures with a low viscosity produce lighter articles withlarger cells within the structural matrix. The formation of the cellularstructural matrix is also dependent on variables such as the solventcontent and the pressure and temperature applied to the mixture. Therheology-modifying agent will also act as a binder to some extent andcan help increase the strength of the article.

Plasticizers, humectants, and porous aggregate may be added to themixture to increase the flexibility of the articles. Typically, once thesolvent is removed to produce the form-stable article, the resultingarticle is very brittle. Plasticizers include materials that can beabsorbed by the starch-based binder to soften the structural matrix andwhich have a sufficiently high vapor point so as not to be vaporized andremoved during the forming process and that will remain stable after thearticle is formed. In addition to water, two preferred plasticizersinclude glycerin and polyethylene glycol. Humectants, such as MgCl₂ andCaCl₂, absorb moisture and tightly bind it with the starch-based bindermolecules so that the bound moisture is not removed during the formingprocess. In turn, the moisture improves the flexibility of the finishedarticle. Porous aggregates can hold the solvent during the formingprocess and then disperse the solvent into the matrix of the form-stablearticle to increase the flexibility of the article. Of course,flexibility may also be imparted to the hardened article through the useof high humidity condition, although this process is not required in allcases.

Calcium sulfate hemihydrate (CaSO₄.1/2H₂ O), the main hydratablecomponent of plaster of paris, may be used as a water absorption agentwithin the mixtures of the present invention because it reacts withwater to form the calcium sulfate dihydrate (CaSO₄.2H₂ O). This bindingof water can be also be utilized as a means for holding waterinternally.

Medium- or long-chain fatty acids, their salts, and their acidderivatives may be added to improve the release of the hardened articlefore the mold. Molds having a polished metal surface, or other non-sticksurface, are also useful in improving or facilitating the release of thearticle.

Although not necessary, other components can be added to the mixture tovary the properties of the final product. Such components includefibers, which improve the fracture energy and toughness of the article,cross-linkers, which improve the strength and stability of the article,and dispersants, which decrease the viscosity of the mixture withoutrequiring an increase in the solvent content.

The articles of the present invention are produced through a multi-stepprocess. Initially, the selected components are blended into ahomogeneous, moldable mixture. The mixing can be carried out in a highenergy mixer or an auger extruder, depending on the viscosity of themixture. It is often preferred to apply a partial vacuum to the mixtureto remove unwanted air voids that can create defects in the finalproduct.

In the preferred embodiment, once the moldable mixture has beenprepared, it is positioned within a heated mold cavity. The heated moldcavity may comprise many different embodiments, including moldstypically used in conventional injection molding processes and die-pressmolds brought together after placing the inorganically filled mixtureinto the female mold. In one preferred embodiment, for example, themoldable mixture is placed inside a heated female mold. Thereafter, aheated male mold is complementarily mated with the heated female mold,thereby positioning the mixture between the molds. As the mixture isheated, the starch-based binder gelates, increasing the viscosity of themixture. Simultaneously, the mixture increases in volume within theheated molds cavity as a result of the formation of gas bubbles from theevaporating solvent, which are initially trapped within the viscousmatrix.

As will be discussed later in greater detail, by selectively controllingthe thermodynamic parameters applied to the mixture (e.g., pressure,temperature, and time), as well as the viscosity and solvent content,the mixture can be formed into a form-stable article having aselectively designed cellular structural matrix. That is, the size,quantity, and positioning of the cells can be selectively designed toproduce articles having desired properties for their intended use.Furthermore, the surface texture and configuration of cells within thestructural matrix can be controlled by selectively varying thetemperature between the molds and the temperature along the length ofthe molds. Besides controlling the properties among different moldedarticles, the properties of a single article can be made to varythroughout the article, including varying thickness, varying skinthickness, varying cell structure, and varying density. This may beaccomplished, for example, by creating within the molding apparatusdifferential relative temperatures, or differential temperature zones,throughout the molding apparatus. As a result, different temperature andprocessing conditions are imparted to varying locations throughout thesame article.

In a preferred embodiment, the articles are formed with the previouslydiscussed admixtures to impart the desired flexibility to the hardenedarticles without the need for conditioning them in high humidity. In analternative embodiment, the hardened articles are placed in a humiditychamber where the articles are exposed to a high humidity environment ata selected temperature. The water molecules in the air are absorbed by,and become bound to through hydrogen bonding, the starch-based binderportion of the matrix, thereby reducing the brittleness of the bindermaterial and imparting the desired flexibility to the articles. It ispreferred to keep the moisture content in the final article to belowabout 10% by weight of the starch-based binder component, as excessmoisture can allow bacterial growth. More preferably, the moisturecontent is kept to below about 5% by weight of the starch-based bindercomponent.

Once the article is conditioned, a coating can be applied. The coatingcan have several purposes, which include providing a finished surface tothe article, sealing the article, and adding additional strength. Thecoating can be applied through various conventional processes such asspraying, dipping, sputtering, and painting. In an alternativeembodiment, selected coating materials can be added to the mixture priorto the formation of the article. If a coating material is used that hasa similar melting point as the peak temperature of the mixture, itmigrates to and coats the surface of the article during the formation ofthe article. Such coating materials include selected waxes andcross-linking agents.

The resulting articles can be designed to have properties similar to orbetter than those of articles made from conventional materials, such aspaper, paperboard, polystyrene, metals, plastic, or other naturalorganic materials. In light of the minimal cost of inorganic fillers andthe moderate cost of starch and flours, the inventive articles can alsobe made at a fraction of the cost of conventional articles. Finally, theinventive articles are more environmentally friendly than conventionalarticles. For example, the manufacturing process uses no harmfulchemicals, emits no harmful emissions into the air or water, depletes nonon-renewable resources, and requires only minimal processing energy.Furthermore, the inventive articles are easily recyclable or quicklydecomposed back into the environment.

From the foregoing, an object of the present invention is to provideimproved inorganically filled compositions for manufacturing articles ofmanufacture that are presently formed from, e.g., paper, paperboard,polystyrene, metals, plastic, or other natural organic materials.

Another object and feature of the present invention is to providecompositions which yield inorganically filled, cellular articles thathave properties similar to those of paper, paperboard, polystyrene,plastic, or metals.

A further object of the present invention is to provide moldablemixtures which can be formed into a variety of articles using the sameor similar manufacturing apparatus and techniques as those presentlyused to form such objects from, e.g., paper, paperboard, metals,polystyrene, plastic, or other organic materials.

Yet another object and feature of the present invention is to providecompositions for manufacturing articles from moldable mixtures which donot result in the generation of wastes involved in the manufacture ofpaper, paperboard, polystyrene, or metal materials.

An additional object of the present invention is to provideinorganically filled, cellular articles that are formed having thedesired flexibility for their intended use.

An additional object of the present invention is to provideinorganically filled, cellular articles where the coating is formedduring the formation of the article.

An additional object of the present invention is to provideinorganically filled, cellular articles that have a smooth and uniformsurface.

A further object of the present invention is to provide compositionswhich contain less water which has to be removed during themanufacturing process (as compared to paper manufacturing) in order toshorten the processing time and reduce the initial equipment capitalinvestment.

Still a further object is to produce articles that are readilydegradable into substances which are nontoxic and commonly found in theearth.

Another object of the present invention is to provide compositions whichmake possible the manufacture of articles at a cost comparable to andeven superior to articles manufactured from existing materials.

A further object and feature of the present invention is the ability tomanufacture starch bound containers and other articles having thedesired flexibility without subjecting them to high humidityconditioning in some cases.

Still another object and feature of the present invention is to providecompositions which are less energy intensive, conserve valuable naturalresources, and require lower initial capital investments compared tothose used in making articles from existing materials.

Finally, an additional object and feature of the present invention is toprovide compositions for mass-producing articles from moldable mixtureswhich can rapidly be formed and ready to use within a matter of minutesfrom the beginning of the manufacturing process.

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto a specific embodiment thereof which is illustrated in the appendeddrawings. Understanding that these drawings depict only a typicalembodiment of the invention and are not therefore to be considered to belimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a phase diagram showing the temperature and pressureconditions that the mixture is subject to in one embodiment of theinvention during formation of the articles.

FIG. 2 is an enlarged cross-sectional view of the skin and interiorsection of a hardened article.

FIG. 2A is a microscopic picture of the cross-section of an articlehaving a thin outside skin and an interior section containing relativelylarge cells.

FIG. 2B is a microscopic picture of the cross-section of an articlehaving a thin outside skin and an interior section containing relativelymedium cells.

FIG. 2C is a microscopic picture of the cross-section of an articlehaving a thick outside skin and an interior section containingrelatively large cells.

FIG. 3 is a cross-sectional view of a male mold and a female mold beingmated.

FIG. 4 is a perspective view of load cells and mixing apparatus.

FIG. 5 is a cross-sectional view of an auger extruder apparatus.

FIG. 6 is a cross-sectional view of a two-stage injector.

FIG. 7 is a cross-sectional view of a reciprocating screw injector.

FIG. 8 is a perspective view of a male mold and a female mold.

FIG. 9 is a cross-sectional view of the female mold being filled with amoldable mixture by a filling spout.

FIG. 10 is a cross-sectional view of the above male mold and female moldbeing mated.

FIG. 11 is a cross-sectional view of the inventive article baked betweenmated molds.

FIG. 11A is an enlarged cross-sectional view of the vent holes betweenthe mated male mold and female mold.

FIG. 12 is a cross-sectional view of the female mold having a scraperblade removing excess material.

FIG. 13 is a cross-sectional view of a dual mold.

FIG. 14 is a cross-sectional view of a split mold with suction nozzle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction

The present invention relates to novel compositions for manufacturingarticles of manufacture from particle packed, inorganically filledmaterials having a starch-based binder and a thermodynamicallycontrolled cellular matrix. The inventive materials can include avariety of environmentally safe components, including a starch-basedbinder, water, inorganic and organic aggregates, mold-releasing agents,fibers, rheology-modifying agents, cross-linkers, plasticizers,dispersants, and coating materials.

A materials science and microstructural engineering approach is used toselect the type, size, shape, and proportion of each component that,when blended together, result in a mixture and subsequent final producthaving desired properties at an optimal cost. The desired properties aredependent on the required handling and the intended use of the finishedarticle. The optimal cost is obtained by selecting components that willmaximize production output while minimizing material and productioncosts.

Using a microstructural engineering approach, the present invention canproduce a variety of articles, including plates, cups, cartons, andother types of containers and articles having mechanical propertiessubstantially similar or even superior to their counterparts made fromconventional materials, such as paper, polystyrene foam, plastic, metaland glass. The inventive articles can also be made at a fraction of thecost of their conventional counterparts. The minimal cost is a result ofthe relatively inexpensive aggregate which typically comprises a largepercentage of the mixture and the minimum processing energy required.

The manufacturing processes and resulting articles are also less harmfulto the environment than conventional processes. For example,theoretically all of the manufacturing waste can be recycled into theproduction line. Once the finished articles have fulfilled theirintended use, the articles, which consist of naturally occurring organicand inorganic materials, are easily decomposed back into the earth, orrecycled. As a result, the inventive articles do not create theenvironmental blight or consume the landfills as do similar articlesmade from conventional materials.

The articles of the present invention are produced by initially blendingselected components into a homogeneous, moldable mixture. The moldablemixture includes a starch-based binder, such as potato, corn, waxy corn,rice, or wheat starch, an inorganic aggregate, such as calciumcarbonate, and a solvent, such as water or alcohol. The shape, sizedistribution, and specific surface area of the inorganic aggregate areselected to maximize the packing density of the mixture and minimize thestarch-based binder and solvent requirements. The addition of highconcentrations of inorganic aggregate filler permits the articles to bemade more quickly, less expensively, more environmentally safe, and witha lower specific heat in comparison to articles made without or withonly low concentrations of inorganic aggregate. Accordingly, thematerials and articles of the present invention are often referred to asbeing "inorganically filled" or "highly inorganically filled."

Admixtures can be combined with the mixture to impart desired propertiesto the articles. For example, rheology-modifying agents and dispersantscan be added to regulate the viscosity of the mixture. High viscositymixtures are used for making dense articles having small cells withinthe structural matrix. Low viscosity mixtures are used for making lowdensity articles having large cells within the structural matrix.Plasticizers, humectants, and porous aggregates can be used forimparting the desired flexibility to the articles during the formingprocess. Other additives include fibers, which increase the fracturetoughness of the article, dispersants, which decrease the viscosity ofthe mixture without the addition of solvent, and selected coatingmaterials, which can form a coating on the articles during the formationprocess. Aggregate particles upon which ettringite has been formed maybe used to improve the interaction between the aggregate particles andstarch-based binder.

Once the moldable mixture is prepared, it is positioned within a heatedmold cavity. The heated mold cavity may comprise many differentembodiments, including molds typically used in conventional injectionmolding processes and die-press molds brought together after placing theinorganically filled mixture into the female mold. In one preferredembodiment, for example, the moldable mixture is placed inside a heatedfemale mold. A heated male mold is then complementarily mated with theheated female mold, thereby positioning the mixture between the molds.By carefully controlling the temperature and pressure applied to themixture, as well as the viscosity and solvent content, the mixture canrapidly be formed into form-stable articles having a selectivelydesigned cellular structural matrix. That is, the surface texture andthe formation of the cells within the structural matrix are selectivelycontrolled by varying the components and their relative concentrationswithin the mixture as well as the thermodynamic processing conditions.The result is the ability to manufacture a wide variety of containersand other articles that have greatly varying thermal and mechanicalproperties corresponding to the performance criteria of the article.

In one embodiment, the articles are formed having the desiredflexibility for their intended use. In an alternative embodiment, theself-supporting articles are placed in a humidity chamber where they areexposed to controlled relative humidity at a selected temperature. Thewater is absorbed by the starch-based binder through hydrogen bonding ofthe water molecules to the hydroxyl groups of the starch, therebysoftening the starch-based binder and imparting the desired flexibilityto the articles. A coating material can be applied either in the mixturebefore the article is formed or the coating can be applied externallyafter the article is formed. Subsequent processing of the articles caninclude printing, stacking, and boxing.

II. Definitions

The terms "inorganically filled mixture," "mixture," or "moldablemixture" as used in the specification and the appended claims haveinterchangeable meanings and shall refer to a mixture that can be formedinto the articles which are disclosed and claimed herein. Such mixturesare characterized by having a high concentration of inorganic filler oraggregate (from about 20% to about 90% by weight of the total solids inthe mixture for most aggregates, and from about 5% to about 85% byvolume of the material in the case of lightweight aggregates), asolvent, and a starch-based binder. The moldable mixtures may alsoinclude other admixtures, such as a mold-releasing agent, fibers,organic aggregates, dispersants, cross-linkers, rheology-modifyingagents, plasticizers, and coating materials.

As used in the specification and the appended claims, the term "totalsolids" includes all solids, whether they are suspended or dissolved inthe mixture. The volume of the total solids does not include theinterstitial voids between the solids, but is calculated by subtractingout the volume of the interstitial voids.

The terms "inorganically filled, cellular matrix", "cellular matrix", or"structural matrix" as used in the specification and the appended claimsare interchangeable and shall refer to matrices of the article afterhardening of the moldable mixture.

Both the moldable mixture and the cellular matrix formed therefrom eachconstitute "inorganically filled, cellular materials" or "inorganicallyfilled materials". These terms as used in the specification and theappended claims are interchangeable and shall refer to materials orcompositions without regard to the amount of solvent or moisture withinthe mixture and without regard to the extent of gelation of thestarch-based binder.

The term "hardening" as used in this specification and the appendedclaims refers to the process of gelation of the starch-based binder andremoval of the solvent to produce a form-stable article. The term"hardening," however, is not limited by the extent of gelation or theamount of solvent removed.

The term "form-stable" as used in the specification and the appendedclaims means that the article has a structural matrix which can beremoved from the mold, support its own weight, and can continue throughsubsequent processing without damaging deformation of the structuralmatrix. Furthermore, the term "form-stable" means that the article hassufficient solvent removed from its matrix so that the article will notbubble or crack as a result of vapor expansion once the article isremoved from the molds. It will be understood, however, that moldedarticles are still considered form-stable even though they may contain asmall percentage of moisture.

III. Conceptual Overview of Formation Process

A. Microstructural Engineering Design

The inorganically filled materials of the present invention aredeveloped from the perspective of microstructural engineering in orderto build into the microstructure of the material certain desired,predetermined properties, while at the same time remaining cognizant ofcosts and other manufacturing complications. Furthermore, thismicrostructural engineering analysis approach, in contrast to thetraditional trial-and-error, mix-and-test approach, has resulted in theability to design inorganically filled materials with those propertiesof strength, weight, flexibility, insulation, cost, and environmentalneutrality that are necessary for the production of functional anduseful containers and other articles.

The number of different raw materials available to engineer a specificproduct is enormous, with estimates ranging from between fifty thousandand eighty thousand. They can be drawn from such disparately broadclasses as metals, polymers, elastomers, ceramics, glasses, composites,and cements. Within a given class, there is some commonality inproperties, processing, and use-patterns. Ceramics, for instance, have ahigh modulus of elasticity, while polymers have a low modulus; metalscan be shaped by casting and forging, while composites require lay-up orspecial molding techniques; hydraulically settable materials, includingthose made from hydraulic cements, historically have low flexuralstrength, while elastomers have high flexural strength and elongationbefore rupture.

Compartmentalization of material properties, however, has its dangers;it can lead to specialization (the metallurgist who knows nothing ofceramics) and to conservative thinking ("we use steel because that iswhat we have always used"). It is this specialization and conservativethinking that has limited the consideration of using inorganicallyfilled materials for a variety of products, such as in the manufactureof containers and other packaging materials.

Nevertheless, once it is realized that inorganically filled materialshave such a wide utility and can be designed and microstructurallyengineered to have desired properties, then their applicability to avariety of possible products becomes appreciable. Such materials have anadditional advantage over other conventional materials, in that theygain their properties under relatively gentle, nondamaging, inexpensiveconditions. (Other materials require high energy, severe heat, or harshchemical processing that significantly affects the material componentsand cost of manufacturing.) Moreover, certain conventional materials, orcomponents thereof, can be incorporated into the materials of thepresent invention with surprising synergistic properties or results.

The design of the compositions of the present invention has beendeveloped and narrowed, first by primary constraints dictated by thedesign, and then by seeking the subset of materials which maximizes theperformance of the components. At all times during the process, however,it is important to realize the necessity of designing products which canbe manufactured in a cost-competitive process.

Primary constraints in materials selection are determined by theproperties necessary for the article to function successfully in itsintended use. With respect to a food and beverage container, forexample, those primary constraints include minimal weight, strength(both compressive and tensile), flexibility, and toughness requirements,while simultaneously keeping the cost comparable to its paper, plastic,polystyrene or metal counterparts.

In its simplest form, the process of using materials science tomicrostructurally engineer and design an inorganically article requiresan understanding of the interrelationships between each of the mixturecomponents, the processes parameters (e.g. time, temperature, pressure,humidity), the mixture properties, and the properties of the finalarticles. By understanding the interrelationships between the variablesat both the macro and micro level, one skilled in the art can selectproportions of desired components that can be processed under selectedconditions to produce articles that have desired properties for anintended use at a minimum cost.

The interrelationships between the variables will be discussed atselected locations in the application where the variables are introducedand defined. Specific compositions are set forth in the examples givenlater in order to demonstrate how the selection of variables canoptimize properties.

B. Articles of Manufacture

Using a microstructural engineering approach, a variety of articles canbe produced from the processes and compositions of the presentinvention. The terms "article" and "article of manufacture" as used inthe specification and the appended claims are intended to include allgoods that can be formed using the disclosed process. Examples of sucharticles of manufacture include containers, such as food and beveragecontainers and packaging containers. Articles within the scope of thisinvention also include such disparate objects as cutlery, flower pots,mailing tubes, light fixtures, ash trays, and game boards.

The terms "container" or "containers," as used in the specification andthe appended claims, are intended to include any receptacle or vesselutilized for, e.g., packaging, storing, shipping, serving, portioning,or dispensing various types of products or objects (including bothsolids and liquids), whether such use is intended to be for a short-termor a long-term duration of time.

Containers within the scope of this invention include, but are notlimited to, the following: cartons, boxes, sandwich containers, hingedor two-part "clam shell" containers, dry cereal boxes, frozen foodboxes, milk cartons, fruit juice containers, carriers for beveragecontainers, ice cream cartons, cups (including, but not limited to,disposable drinking cups, two-piece cups, one-piece pleated cups, andcone cups), french fry containers used by fast-food outlets, fast-foodcarry out boxes, packaging, support trays (for supporting products suchas cookies and candy bars), cans, yoghurt containers, sleeves, cigarboxes, confectionery boxes, boxes for cosmetics, plates, vending plates,pie plates, trays, baking trays, bowls, breakfast plates, microwaveabledinner trays, "TV" dinner trays, egg cartons, meat packaging platters,disposable single use liners which can be utilized with containers suchas cups or food containers, substantially spherical objects, bottles,jars, cases, crates, dishes, medicine vials, and an endless variety ofother objects.

The container should be capable of holding its contents, whetherstationary or in movement or handling, while maintaining its structuralintegrity and that of the materials contained therein or thereon. Thisdoes not mean that the container is required to withstand strong or evenminimal external forces. In fact, may be desirable in some cases for aparticular container to be extremely fragile or perishable. Thecontainer should, however, be capable of performing the function forwhich it was intended. The necessary properties may always be designedinto the material and structure of the container beforehand.

The container should also be capable of containing its goods andmaintaining its integrity for a sufficient period of time to satisfy itsintended use. It will be appreciated that, under certain circumstances,the container may seal the contents from the external environments, andin other circumstances may merely hold or retain the contents.

Containment products used in conjunction with the containers are alsointended to be included within the term "containers." Such productsinclude, for example, lids, straws, interior packaging, such aspartitions, liners, anchor pads, corner braces, corner protectors,clearance pads, hinged sheets, trays, funnels, cushioning materials, andother object used in packaging, storing, shipping, portioning, serving,or dispensing an object within a container.

The containers within the purview of the present invention may or maynot be classified as being disposable. In some cases, where a stronger,more durable construction is required, the container might be capable ofrepeated use. On the other hand, the container might be manufactured insuch a way so as to be economical for it to be used only once and thendiscarded. The present containers have a composition such that they canbe readily discarded or thrown away in conventional waste landfill areasas an environmentally neutral material.

The articles within the scope of the present invention can have greatlyvarying thicknesses depending on the particular application for whichthe article is intended. They can be as thin as about 1 mm for uses suchas in a cup. In contrast, they can be as thick as needed where strength,durability, and or bulk are important considerations. For example, thearticle may be up to about 10 cm thick or more to act as a specializedpacking container or cooler. The preferred thickness for most articlesis in a range from about 1.5 mm to about 1 cm, with about 2 mm to about6 mm being most preferred.

The phrases "mass-producible" or manufactured in a "commercial" or"economic" manner are intended in the specification and the appendedclaims to refer to the capability of rapidly producing articles at arate that makes their manufacture economically comparable to articlesmade from conventional materials, such as paper, paperboard,polystyrene, plastic, or metal.

The containers and other articles made from inorganically filledmaterials are intended to be competitive in the marketplace with sucharticles currently made of various materials, such as paper, plastic,polystyrene, or metals. Hence, the articles of the present inventionmust be economical to manufacture (i.e., the cost will usually notexceed a few cents per item). Such cost restraints thus requireautomated production of thousands of the articles in a very short periodof time. Hence, requiring the articles of the present invention to beeconomically mass-produced is a significant limitation on the qualitiesof the materials and products.

C. Processing Concepts and Variables

The present section discusses the underlying concepts and processingvariables used in manufacturing the articles of the present invention. Adetailed description of the mechanical apparatus used in themanufacturing process will be provided later in the disclosure.

The mixture of the present invention is prepared by combining selectedcomponents and blending them until a homogeneous, moldable mixture isformed. The dry components are typically mixed first. The liquidcomponents, such as water, are then blended into the mixture. In oneembodiment, the mixture is prepared in a sealed chamber to which anegative pressure or vacuum is applied. The applied vacuum both removesand prevents the entrainment of air bubbles within the mixture. Theadvantage of this is because entrained air bubbles tend to migrate tothe exterior surface of the article during the forming process, whichmay result in a product having increased surface defects and lowerstructural integrity.

Once the mixture has been prepared, it is formed or molded into theshape of the desired article. In one embodiment, the forming stepsinclude positioning and locking the mixture between a heated male moldhaving a desired shape and a heated female mold having a complementaryshape. The heat from the molds causes the mixture to expand within themolds. Excess material and vapor is expelled from between the moldsthrough small vent holes. Once a sufficient amount of the solvent hasbeen removed, the molds are opened, and the form-stable article having acellular structural matrix is removed for subsequent processing.

The process is more accurately defined through the use of a phasediagram. Depicted in FIG. 1 is a phase diagram for water. FIG. 1illustrates, by way of a general example, the pressure and temperaturestages that a mixture using water as a solvent undergoes duringformation of the article. Between points A and B along line 1, themixture is locked between the molds and is rapidly heated at first atconstant ambient pressure to a temperature of about 100° C. The portionof the mixture closest to the molds is heated at a faster rate and thusreaches a temperature of 100° C. before the interior section of themixture. As the mixture begins to heat, the starch-based binder beginsto gelate, increasing the viscosity of the mixture. (The process ofgelation is discussed later in the section on starch-based binders.)

Once the temperature of the water within the moldable mixture in contactwith the mold surface reaches 100° C., the water begins to vaporize,thereby forming air pockets or voids within the mixture. As a result ofthese expanding pockets, the volume of the mixture expands, causing themixture to "rise," which thereby the mold and momentarily clogging thesmall vent holes. The water or solvent within the portion of themoldable mixture closest to the molds is quickly vaporized and drivenoff from the mixture at or near the region closest to the mold, asrepresented in FIG. 1 by point B, thereby hardening that portion of themixture into a thin, dense skin. The skin is believed to be formedalmost instantaneously and acts as an insulation barrier for theremaining portion of the moldable mixture, thereby slowing down the rateof heating. With the vent holes plugged, and due to the restricted flow,the pressure begins to increase between the molds, as shown by line 2,preventing the transformation of the remaining solvent into vapor at theboiling point, which is usually 100° C. for water. Instead, as alsoshown by line 2, the solvent in the moldable mixture is super heated asa result of the restricted flow. Eventually, the material blocking thevent holes ruptures, allowing excess material to escape from between themolds. However, as a result of the small size of the vent holes, theflow of the escaping mixture is restricted, thereby allowing thepressure and temperature within the mold to further increase to point Con FIG. 1.

The cellular structural matrix is formed when sufficient excess materialhas escaped to cause the pressure to drop between the molds. Under highpressure the solvent vapor which forms is nucleated because ofsuperheating. The drop in pressure causes the superheated solvent totransform rapidly into the gaseous state through an adiabatic expansion,thereby forming a distribution of voids or cells throughout thestructural matrix of the article. The tendency of the solvent vapor tobecome nucleated at individual points throughout the superheated mixtureyields a fairly well-distributed cell structure. The transformation ofthe solvent to vapor is an endothermic reaction that absorbs heat fromthe moldable mixture, thereby substantially decreasing the temperatureof the moldable mixture inside the mold. The drop in temperature andpressure of the moldable mixture is depicted by line 3 extending frompoint C to B. The illustration that the temperature of the mixturereturns to 100° is simply by way of example. In actuality, thetemperature of the mixture may drop below 100° C. The drop in pressureof the solvent is depicted as line 5 extending from point C to D.

With the vent holes open and the pressure reduced, the mixture thenbegins to heat up again to the boiling point of the solvent, allowingthe remaining solvent to freely evaporate until sufficient solvent hasbeen removed for the article to become form-stable. This process isdepicted by line 5 extending from point B. This analysis of the cellularformation is supported by the fact that producing articles under lowpressure results in articles having minimal voids. For example,gradually evaporating the solvent from the mixture at a low temperatureor heating the mixture rapidly on top of a single mold results in aproduct having a lower concentration of air voids and high density.

Depicted in FIG. 2 is a microscopic image of a cross-section 8 of aformed article. The figure reveals the present articles as having anoutside skin 10 with small cells 12 and an interior section 14containing large cells 16. Small cells 12 are defined as having anaverage diameter of less than about 250 μm. The material betweenadjacent cells is referred to as a cell wall 18. The distribution andsize of the cells within the structural matrix are dependent on severalvariables including the viscosity of the mixture, temperature of themolds, and composition of the mixture, i.e., types and amounts ofsolvent, starch-based binder, aggregate, rheology-modifying agent, andother admixtures.

Articles can be made having a desired structural matrix by controllingthe related variables. For example, FIG. 2A is a microscopic picture ofthe cross-section of an article having a thin outside skin 10 and largecells 16 located in interior section 14. FIG. 2B is a microscopicpicture of the cross-section of an article having a thin outside skin 10and medium cells 19 located in interior section 14. Finally, FIG. 2C isa microscopic picture of the cross-section of an article having a thickoutside skin 10 and large cells 16 located in interior section 14. Ingeneral, the insulation ability and the strength of the structuralmatrix of the article increase as the cells become more evenly dispersedthroughout the matrix. Increasing the overall volume of the cellularspace also would tend to improve the insulation ability, although itwould be expected to have an adverse effect on the strength of thematrix. The insulation ability can be improved without significantlysacrificing strength by adding an efficiently particle packed,lightweight aggregate to the matrix.

The size of the cells within the structural matrix is heavily influencedby the viscosity and/or state of hardening of the article. As previouslydiscussed, outside skin 10 is formed early on in the process and isimportant for the structural integrity of the article. Accordingly, whenthe pressure drops and the cells are formed within the mixture, it ismuch easier for the vapor to expand within interior section 14 than inoutside skin 10. Thus, the cells are much larger within interior section14. It is also possible that the cells in outside skin 10 are formed atthe same time the skin is formed. That is, as the solvent vaporizeswithin the portion of the mixture forming outside skin 10, small bubblesbegin to form within the skin. However, the outside portion of themixture is heated so quickly that the skin becomes hard before the cellshave a chance to enlarge.

As stated above, it is important to remove enough solvent so that thearticle can be removed from the mold and be adequately form stable. Ingeneral, the structural matrix of the molded articles will contain about5% or less solvent at the point where the article has adequate strengthand stability to be demolded. The need to remove this relatively highquantity of solvent in order to create a form stable article that can bedemolded properly results from the tendency of the vaporized solventwithin the cellular matrix to further expand after the demolding step.Thus, an inadequately dried article has a tendency to "blow up" upondemolding due to the high internal pressure of the vaporized solvent.

However, this high internal pressure can be greatly reduced by theapplication of a cooling cycle immediately following the heating cyclebefore the article is demolded. Cooling the structural matrix of thearticle causes the solvent to recondense, thereby reducing the internalpressure caused by the vaporizing solvent during the heating cycle. Theapplication of a cooling cycle allows for the demolding of the articlewhile maintaining adequate internal moisture to maintain flexibility andresilience, which, in turn, obviates the need for a subsequentconditioning step.

The viscosity of the mixture during the formation process is a functionof the composition of the mixture and the processing parameters. As willbe discussed later in the section on compositions, the viscosity of themixture can be selectively adjusted by the types of starch-based binderand the amount of solvent added. Rheology-modifying agents anddispersants are also used to control the viscosity. By using mixtureshaving a low viscosity, the vapor formed by the solvent can more easilyexpand, thereby producing low-density articles having large cells.Mixtures having a high viscosity make it more difficult for the vapor toexpand, thereby producing denser articles having smaller cells.

In one embodiment, in order to control the cell size the mixture ispre-cooked before being formed into the desired shape. The moldablemixture is pre-cooked by heating the mixture, such as by a pressurecooker or microwave, to the point of gelation of the starch-basedbinder. The exact temperature depends on the type of starch-based binderbeing used. For example, potato starch gelates at about 65° C. Bygelating the starch-based binder before positioning it between themolds, the amylose polymers within the starch granules are better ableto extend and fully intertwine before hardening. Furthermore, theviscosity of the mixture is higher when first placed between the molds.As a result, the finished article has increased strength and smaller,more uniform cells. As will be discussed later, different types ofstarch-based binder have different effects on the formation of thecells.

The processing variables associated with the formation of the inventivearticles and the cellular structural matrix include mold temperature,time for removing the solvent, filling volume, vent hole size, and thecycles of opening and closing of the molds prior to locking of themolds. The articles of the present invention are preferably removed fromthe locked molds after most, but not all, of the solvent (typicallygreater than about 95%) has been removed. While the mixture is lockedbetween the molds, the outside edges of the articles are supported bythe opposing molds. Vapor formed by the evaporation of the solvent isthus forced to travel under pressure to the vent holes, where it isexpelled. The outside walls of the article are the first to form and arebrittle as a result of the loss of water. Separation of the molds priorto removing substantially all of the solvent permits the vapor to expandbetween the article walls, resulting in bubbling, cracking, ordeformation of the outside walls of the articles. Furthermore, attemptsto remove the article from the molds prior to removal of a sufficientamount of moisture can result in the article sticking to the molds anddamage to the structural matrix.

Since the article cannot be removed until after the solvent has beensubstantially removed, it is preferable to have the mold temperature ashigh as possible. This minimizes the time for removal of the solvent andpermits the quickest production of articles. Studies, however, havefound that temperatures above about 240° C. result in dextrification orbreaking down of the starch molecules in the surface of the article.Dextrification carmelizes the starch, produces a brown color on thearticle, and reduces the structural integrity of the article.Temperature above about 240° C. can also burn certain organic fibers ifused. In addition, overdrying the molded articles leads to shrinkage andcracking. Some amount of moisture should, therefore, remain within thestructural matrix of the article.

In contrast, it is difficult to form an article having a cellularstructural matrix at mold temperatures below about 120° C. At such lowtemperatures, there is little pressure build-up and only slowevaporation of the solvent. Studies have found that increasing theprocessing temperature to between about 140°-240° C. decreases theproduction time and the density of the article. With temperaturesranging between 140°-180° C., the decrease in production time issubstantial. After about 180° C., however, the decrease in processingtime is rather limited. Again, this finding is consistent with thecellular formation model. The higher temperatures result only in amarginal decrease in the formation time because they only marginallyshorten the incubation period before the drop in pressure and they onlymarginally shorten the time for removing the moisture after the cellularstructure is formed. The temperature of the molds has little, if any,significant effect on the rate of formation of the cells after the dropin pressure.

As the temperature increases, the size of the cells also increases. Thesize of the cells within the structural matrix, and thus the strengthand insulating capability of the articles, can thus be selected in partby adjusting the temperature of the molds. Furthermore, by varying thetemperature differential between the male and female molds, the cellsize can be selectively varied between the walls of the article. Forexample, by making the female mold hotter than the corresponding malemold, a cup can be formed having relatively large cells and higherinsulating capability at its outside surface where the cup is held. Incontrast, the cup will be more dense and be more water tight at itsinside surface where liquid will be held.

A temperature of 200° C. is preferred for the rapid production ofthin-walled articles, such as cups. Thicker articles require a longertime to remove the solvent and are preferably heated at lowertemperatures to reduce the propensity of burning the starch-based binderand fiber. Leaving the articles within the locked molds too long canalso result in cracking or deformation of the articles. It is theorizedthat removing greater than about 98% of the solvent within the mixtureresults in shrinking of the structural matrix, which in turn can crackthe article. Accordingly, the article is optimally removed from the moldwhen approximately 2%-5% of the moisture remains within the article. Itshould be understood, however, that these figures are only roughapproximations.

The temperature of the mold can also effect the surface texture of themolds. Once the outside skin is formed, the solvent remaining within theinterior section of the mixture escapes by passing through minuteopenings in the outside skin and then travelling between the skin andthe mold surface to the vent holes. If one mold is hotter than theother, the laws of thermodynamics would predict, and it has beenempirically found, that the steam will tend to travel to the coolermold. As a result, the surface of the article against the hotter moldwill have a smoother and more uniform surface than the surface againstthe cooler mold.

The temperature of the molds can also be varied along the length of themolds. Depicted in FIG. 3 is a male mold 15 mated with a female mold 17,with a moldable mixture being positioned therebetween. In general, themale mold includes a top end 6 and a bottom end 7. Likewise, the femalemold includes a top end 9 and a bottom end 11. Located near top ends 6and 9 are vent holes 13, through which the excess material and vapor canescape. Studies have found that for deep recessed articles such as cups,a smoother surface and more uniform structural matrix can be obtained ifthe mixture is hardened sequentially from the point furthermost from thevent hole to the point closest to the vent holes. For example, referringto FIG. 3, it is preferable in some cases for the temperature of themolds to be the highest at bottom ends 7 and 11, with the temperaturegradually decreasing toward top ends 6 and 9, where the temperature isthe lowest.

Such a temperature zone differential within the molds helps to directthe vapor and air out the vent holes. As the solvent is vaporized at thebottom end of the molds, the vapor is absorbed into the adjacentmixture. The vapor thus gradually travels to the vent holes.Furthermore, since the mixture closest to the vent holes is the last toharden, the excess material is more easily expelled from between themolds. In contrast, if the molds were hottest near top ends 6 and 9, thevapor near bottom ends 7 and 11 would be forced to travel over thealready hardened surface of the article, thereby possibly damaging thesurface texture. Likewise, the excess material would already be hardenedand its removal could result in disrupting the structural integrity ofthe article.

The mold temperature and the time for removing the solvent areinterdependent and are further dependent on the thickness of the articleand the amount of solvent present. The mold temperature of the presentinvention is preferably in a range from about 150° C. to about 220° C.,with about 170° C. to about 210° C. being more preferred, and from about190° C. to about 200° C. being most preferred. However, thicker articlesmay require lower temperatures. The time in which the solvent ispreferably removed from the mixture ranges from about 1 second to about15 minutes, with about 15 seconds to about 5 minutes being morepreferable, and from about 30 seconds to about 1 minute being mostpreferable. It should be noted that in light of the endothermic processof the vaporization of the solvent and the rather short period of timethat the molds are in contact with the mixture, the mixture within theinterior of the molded article generally does not get as hot as themolds. Typically, the temperature of the mixture will not exceed about130° C.

The volume of material positioned between the molds for subsequentheating also affects the resulting density of an article. If not enoughmaterial is introduced into the mold to form a complete article (noexcess material is discharged) the resulting material will have a higherdensity and moisture content. This results from a lack of pressure buildup and subsequent expansion. When sufficient material is added toproduce the desired pressure (a minimum of excess material) the densityof the article dramatically decreases.

Further increases in the amount of material will decrease the density ofthe article up to a point. Past this point, the addition of morematerial will have little or no further effect on the resulting density.For example, in the production of 12 oz. cups, the addition of 1 gram ofextra material resulted in a decrease in density of about 0.005 g/cm³.However, adding more than 35 grams of material resulted in no furtherdecrease in the density and was merely wasted.

The pressure buildup within the molds is dependent both on thetemperature of the molds and the size of the vent holes. The larger thevent holes, the less pressure that builds within the moldable mixture,resulting in less expansion and a more dense structural matrix of themolded article. Accordingly, the larger the vent holes, the smaller thecells within the structural matrix. However, if the vent holes are toolarge, the mixture will not be able to plug the vent holes, therebypreventing the required pressure buildup for the formation of thedesired cell structure. (Such an arrangement may be preferred, however,if a more dense article is desired.) Another drawback to large ventholes is that they can create larger deformities on the surface of thearticles at the point where the excess material is removed. The size ofthe deformities can be reduced by decreasing the size and increasing thenumber of the vent holes.

If the vent holes are too small, an excessive pressure will build up,resulting in deformation or even explosion of the article upon releaseof the pressure. The size of the cells can further be regulated bycontrolling the release of pressure. For example, by slowing down therate of pressure drop, the sudden expansion force caused by vaporizationof the solvent is decreased. This results in articles having smallercells and thicker cell walls, which together produce a stronger article.

As previously discussed, by regulating the size of the vent holes, thesize of the cells in the structural matrix can be regulated. The exactsize and number of vent holes depends on the size of the article beingproduced. Larger articles require more vent holes. Examples of ventsizes and numbers to produce articles is shown later in the applicationin the Example Section. In the production of most articles of thepresent invention, the vent sizes will preferably range from about 0.05mm² to about 15 mm², more preferably from about 0.2 mm² to about 5 mm²,and most preferably from about 0.5 mm² to about 2 mm². The number ofvent holes will preferably be in a range from about 1 to about 10, withabout 2 to about 8 being more preferred, and about 4 to about 6 beingmost preferred. In a preferred method for manufacturing cups, it hasbeen found that using 4 vent holes, each having a vent hole of about 1.9mm², is preferred.

Cyclic separation of the molds is used to produce articles havingincreased skin thickness and density over a faster heating time. Thestep of cyclic separation is performed immediately after the mixture ispositioned between the molds and includes the repeated steps of slightlyraising or separating the molds and then bringing them back together. Byseparating the molds, vapor is permitted to easily and quickly escapethrough the sides of the molds, as opposed to having to be forcedthrough the vent holes. Releasing the vapor helps to dry out themoldable material, which in turn increases the skin thickness of theresulting article. Once the step of cyclic separation is completed, themolds are locked and the process of forming the cellular article iscompleted with the remaining amount of solvent in the mixture.

As will be discussed later in greater detail, by decreasing the amountof solvent in the mixture through cyclic separation, the resultingarticle will have a higher density. Cyclic separation also permits thesolvent to escape at a faster rate, thereby yielding an article in ashorter period of time. However, if speed is the only consideration, themixture can initially be made with less solvent, and thus lessen oreliminate the need for cyclic separation of the molds.

The variables associated with cyclic separation include the time themolds are open, the time the molds are closed between openings, thenumber of separations, and the distance the molds are separated.Depending on the desired properties of the articles, the time the moldsare opened and the time they are closed during the cyclic separation(which do not have to be the same) are each in a preferred range fromabout 0.2 seconds to about 5 seconds, with 0.3 seconds to about 1 secondbeing more preferred, and from about 0.4 seconds to about 0.7 secondsbeing most preferred. The number of separations is typically in apreferred range from about 1 to about 20, with about 3 to about 10 beingmore preferred, and about 4 to about 7 being most preferred. Finally,the separation distance will preferably be within a range from about 1mm to about 25 mm, with about 2 mm to about 10 mm being more preferred,and about 3 mm to about 5 mm being most preferred.

As will be discussed later in greater detail, selected admixtures suchas humectants or plasticizers can be added to the mixtures to impartdesired flexibility to the article during the forming step. If no suchadmixtures are combined with the mixture, and as a result of the removalof substantially all the solvent from the mixture, the article removedfrom the molds is often brittle and may be cracked or crushed. Toinstill the necessary flexibility and deformation-before-cracking tomake the article useful, moisture is incorporated back into thestarch-bound structural matrix. This process is referred to as"conditioning." The moisture is preferably applied by placing thearticle within a high humidity chamber at a predetermined temperatureand humidity. Moisture within the highly humid environment is absorbedby the starch-based binder. The moisture softens the starch-based binderand increases the flexibility of the article. Since the starch-basedbinder has a natural affinity for water, the article can be conditionedby simply exposing the article to normal environmental conditions. Overtime, the article will absorb moisture from the air until it reaches apoint of equilibrium. However, depending on the humidity in the air,such a process can take hours, days, or even weeks. Furthermore, in verydry climates, there may be insufficient moisture in the air toadequately condition the article.

The use of a humidity chamber speeds up the process to within a matterof minutes, making it possible to mass-produce the articles. Thevariables associated with the humidity chamber include time,temperature, and humidity. Studies have found that higher humidities upto about 95% are preferred, as they decrease the amount of timenecessary for the article to absorb sufficient moisture. It ispreferred, however, that water not be directly applied to the article,nor should the humidity be so high that water condenses on the article.The application of water directly onto the surface of the article cancause the starch-based binder to swell, thereby forming an irregularityon the surface of the article. Accordingly, the humidity within the highhumidity chamber of the present invention will preferably be in a rangefrom about 50% to about 95%, with about 75% to about 95% being morepreferred, and about 85% to about 95% being most preferred.

Although increasing the temperature in the humidity chamber alsoincreases the rate of absorption of moisture, if the article absorbsmoisture at an excessive rate, the exterior will become unstable andlose its shape prior to the interior of the article obtaining therequired moisture content. Furthermore, it is difficult and expensive toobtain humidity chambers that can create an environment having both hightemperature and humidity. Accordingly, the temperature within thehumidity chamber will preferably be in a range from about 30° C. toabout 60° C., with about 35° C. to about 55° C. being more preferred,and from about 40° C. to about 50° C. being most preferred.

The time in which the articles remain in the humidity chamber is, ofcourse, dependent on the temperature and humidity level. Most articlesobtain desired properties with a moisture content of less than about 20%by weight of the article. The present articles can be manufacturedhaving a moisture content preferably in a range from about 2% to about20% by weight of the article, with about 2% to about 15% being morepreferred, and about 4% to about 10% being most preferred. As will bediscussed later in greater detail, the required moisture content is inpart dependent on the concentration of inorganic fillers in thearticles. The time period for an article to obtain the desired moisturecontent is also dependent on the thickness of the article. The thickerthe article, the longer it will take for the moisture to penetrate tothe center of the article. The rate of absorption and the necessarymoisture content to yield an article with the desired properties arealso dependent on the type and quantity of filler, which will bediscussed later in the section on aggregates.

From a health standpoint, it is desirable to minimize the moisturecontent in an article, preferably to below about 10%. The lower themoisture content, the less chance of bacterial growth in the article andmold formation on the surface. This is especially important for food andbeverage containers. Furthermore, absorbing too much moisture can causethe article to become unstable. Based on the above parameters fortemperature and humidity, the present articles are preferably left inthe humidity chamber for a period of time in a range from about 1 minuteto about 30 minutes, with from about 5 minutes to about 15 minutes beingmore preferred, and from about 5 minutes to about 10 minutes being mostpreferred. Such periods, however, can be extended for very thickarticles and shortened for very thin articles.

Using the above processes in conjunction with the mixture componentsoutlined below, cellular articles of the present invention arepreferably manufactured to have a density in a range from about 0.05g/cm³ to about 1 g/cm³, with about 0.1 g/cm³ to about 0.5 g/cm³ beingmore preferred, and about 0.15 g/cm³ to about 0.25 g/cm³ being mostpreferred.

The remaining processing steps include optional steps, such as printingand coating. These steps, along with stacking, bagging, and boxing, areperformed substantially identically to that of conventional articlesmade from materials such as paper, plastic, polystyrene foam, and otherorganic materials. These steps are discussed later in the disclosure.

IV. Compositional Effects of Formation

To facilitate implementation of the microstructural engineeringapproach, each of the components in the moldable mixture is discussed.The discussion includes the properties and preferred proportions of eachof the components, along with how each component is interrelated withprocessing parameters, properties of the moldable mixture, andproperties of the final article.

A. Starch-Based Binders

The moldable mixtures used to manufacture the inorganically filled,cellular articles of the present invention develop their strengthproperties through the gelation and subsequent drying out ofsubstantially solvated starch-based binder. Starch is a naturalcarbohydrate chain comprising polymerized sugar molecules (glucose).Plants manufacture and store the starch as food for itself and forseeds. Starch is formed in granules that comprise two types of glucosepolymers: the single-chain amylose that is soluble in water and othersolvents and the branched amylopectin that is insoluble in water.

In general, starch granules are insoluble in cold water; however, if theouter membrane has been broken by, e.g., grinding, the granules canswell in cold water to form a gel. When the intact granule is treatedwith warm water, the granules swell and a portion of the soluble starch(amylose) diffuses through the granule wall to form a paste. In hotwater, the granules swell to such an extent that they burst, resultingin gelation of the mixture. The exact temperature at which astarch-based binder swells and gelates depends on the type ofstarch-based binder.

Gelation is a result of the linear amylose polymers, which are initiallycompressed within the granules, stretching out and cross-linking witheach other and with the amylopectin. After the water is removed, theresulting mesh of inter-connected polymer chains forms a solid materialthat can have a tensile strength up to about 40-50 MPa. The amylosepolymers can also be used to bind individual aggregate particles andfibers within the moldable mixture (thereby forming a highlyinorganically filled matrix). Through careful microstructuralengineering, highly inorganically filled containers and other articlescan be designed having desired properties including flexural strengthsup to about 8 MPa.

Although starch is produced in many plants, the most important sourcesare seeds of cereal grains (e.g., corn, waxy corn, wheat, sorghum, rice,and waxy rice), which can also be used in the flour and cracked state.Other sources include tubers (potato), roots (tapioca (i.e., cassava andmaniac), sweet potato, and arrowroot), and the pith of the sago palm.

As used in the specification and the appended claims, the term "starch"or "starch-based binder" includes unmodified starches (amylose andamylopectin) and modified starches. By modified, it is meant that thestarch can be derivatized or modified by typical processes known in theart such as, e.g. esterification, etherification, oxidation, acidhydrolysis, cross-linking, and enzyme conversion. Typical modifiedstarches include esters, such as the acetate and the half-esters ofdicarboxylic acids/anhydrides, particularly the alkenylsuccinicacids/anhydrides; ethers, such as the hydroxyethyl and hydroxypropylstarches; oxidized starches, such as those oxidized with hypochlorite;starches reacted with cross-linking agents, such as phosphorusoxychloride, epichlorohydrin, hydrophobic cationic epoxides, andphosphate derivatives prepared by reaction with sodium or potassiumorthophosphate or tripolyphosphate, and combinations thereof. Modifiedstarches also include seagel, long-chain alkylstarches, dextrins, aminestarches, and dialdehyde starches. Unmodified starch-based binders aregenerally preferred over modified starch-based binders because they aresignificantly less expensive and produce comparable articles.

Pre-gelatinized starch-based binders can also be added to the moldablemixture. Pregelatinized starch-based binders are starches that havepreviously been gelated, dried, and ground back into a powder. Sincepre-gelatinized starch-based binders gelate in cold water, suchstarch-based binders can be added to the moldable mixture to increasethe mixture viscosity prior to being heated. The increased viscosityprevents settling and helps produce thicker cell walls as will bediscussed later in greater detail. In such cases, the pre-gelatedstarch-based binder might be considered to be acting as arheology-modifying agent.

Preferred starch-based binders are those that gelate and produce a highviscosity at a relatively low temperature. For example, potato starchquickly gelates and reaches a maximum viscosity at about 65° C. Theviscosity then decreases, reaching a minimum at about 95° C. Wheatstarch acts in a similar fashion and may be preferred, depending on costand availability. Such starch-based binders are valuable in producingthin-walled articles having a smooth surface and a skin with sufficientthickness and density to impart the desired mechanical properties.

As previously discussed, the portion of the moldable mixture closest tothe heated molds is rapidly heated. By using a mixture containing potatostarch, the portion of the moldable mixture closest to the heated moldsis at a maximum viscosity during drying and formation of the cellularstructure. Accordingly, the cells near the sides of the article have aminimum cell size and a maximum cell wall thickness. In contrast, thecellular structure in the moldable mixture at the interior section ofthe article is not formed until after the viscosity has decreased. As aresult, the cells in the interior section are much larger. This theoryis consistent with the formation of the cellular matrix as previouslydescribed.

It may be preferred to combine different types of starch-based bindersto regulate the cellular matrix. In contrast to potato starch, theviscosity of a mixture containing corn starch gradually increases as thetemperature increases. Accordingly, corn starch produces a relativelylow viscosity mixture compared to potato starch at 65° C., but producesa relatively high viscosity mixture compared to potato starch at 95° C.By combining both corn starch and potato starch within the same mixture,the viscosity of the mixture at the interior section of the article isincreased at the point when the cells are formed. The increasedviscosity decreases the cell size and increases the cell wall thickness,thereby increasing the fracture toughness of the article.

The concentration of starch-based binder within the moldable mixtures ofthe present invention are preferably in a range from about 10% to about80% by weight of total solids, more preferably in a range from about 30%to about 70%, and most preferably from about 40% to about 60% by weight.Furthermore, combinations of different starches may be employed to morecarefully control the viscosity of the mixture throughout a range oftemperatures, as well as to affect the structural properties of thefinal hardened article.

B. Solvent

A solvent is added to the moldable mixture in order to lubricate theparticles, solvate or at least disperse the starch-based binder, and actas an agent for gelating the starch-based binder. A preferred solvent iswater, but can include any liquid that can disperse and gelate thestarch-based binder and be subsequently removed form the moldablemixture.

The amount of heat energy required to remove the solvent must be greatenough to overcome the boiling point of the solvent being used. Besidesboiling at 100° C., water has a relatively large heat of vaporizationcompared to most other solvents, including alcohols. Both the boilingpoint and the heat of vaporization of water can be reduced through theaddition of alcohol co-solvents with the water. Alcohols, such asethanol and isopropyl alcohol, are preferable because they form lowerboiling point azeotropic mixtures with water and are relativelyinexpensive and readily available. Production costs may be optimized byusing a mixture of water and alcohol as long as the benefits of usingalcohol co-solvents, such as the savings in time and energy, are notoutweighed by the increased cost of the alcohol.

The solvent also serves the function of creating a moldable mixturehaving the desired rheological properties, including viscosity and yieldstress. These properties are general ways of approximating the"workability" or flow properties of the moldable mixture. The viscosityof the mixtures of the present invention may range from being relativelylow (similar to that of a thin batter) up to being very high (similar topaste or clay). Where the viscosity is so high that the material isinitially moldable and dough-like in the green state, it is generallybetter to refer to the yield stress, rather than the viscosity, of themixture. The yield stress is the amount of force necessary to deform themixture. As will be discussed later, the amount of solvent required toimpart a certain viscosity and/or yield stress to the mixture is highlydependent on the packing density and specific surface area of theaggregate material. These are also dependent on the addition ofadmixtures, such as rheology-modifying agents and dispersants.

At a minimum, a sufficient amount of the solvent should be added todisperse and uniformly gelate the moldable mixture. The solvent contentshould also be sufficient to function with the processing equipment. Aswill be discussed later in greater detail, moldable mixtures with highviscosity and yield stress may require an auger apparatus to mix andconvey the mixture to the mold. In contrast, low viscosity mixtures canuse conventional mixers to combine the components and pumps to transferthe mixture.

Increasing the solvent content also increases the number and size of thecells in the structural matrix and lowers the density of the resultingarticle. In theory, the more solvent in a mixture, the more vapor thatis produced, and thus, the more cells that are formed. Furthermore, themore solvent in a mixture, the lower the viscosity of the mixture, andthus, the larger the size of the cells. However, the more solvent addedto a mixture, the more time and energy required to remove the solvent,and thus, the slower and more expensive the process. In addition, if thesolvent content gets too high, the mixture may be unable to produceform-stable, crack free articles. In contrast, using low water yields amore dense product having smaller cells.

Very low viscosity mixtures can also result in settling of thecomponents, most notably the ungelated starch-based binder and aggregateparticles. Settling may occur in the mixing stage, transfer stage, orforming stage. Settling can yield articles having varying propertiesfrom batch to batch or within the structural matrix of a single article.Experiments have also found that very low viscosity mixtures can splashout of the female mold during mating with the male mold. This isespecially true for shallow articles such as plates.

Based on the above discussion, the percentage of solvent in the mixturedepends, in part, on the processing equipment, the desired viscosity,and the desired properties. The amount of solvent added to the mixturesof the present invention will preferably be in a range from about 20% toabout 70% by total weight of the mixture, more preferably from about 30%to about 60%, and most preferably from about 40% to about 50%.

As stated above, the viscosity of the moldable mixture is dependent onseveral variables such as the water content, the presence of admixturessuch as rheology-modifying agents and dispersants, whether thestarch-based binder has been pre-cooked, and the packing density of theaggregate. Functional articles can be made from moldable mixtures havinga large range of viscosities, from as low as about 0.05 Pa.s to as highas about 10¹⁰ Pa.s. Low viscosity mixtures can be poured into themolding apparatus while high viscosity mixtures may be placed into themolds by auger or piston insertion. Furthermore, high viscosity mixtureshaving a consistency similar to that of clay or dough can be cut intosmall portions which can then be mechanically placed between the molds.In general, the moldable mixtures of the present invention willpreferably have a viscosity in a range from about 0.01 Pa.s to about 300Pa.s, more preferable from about 0.05 Pa.s to about 30 Pa.s, and mostpreferably from about 0.2 Pa.s to about 3 Pa.s. The rheology of themoldable mixtures may also be described in terms of yield stress, whichwill preferably range up to about 500 kPa, more preferably up to about300 kPa, and most preferably up to about 100 kPa.

C. Aggregates

The terms "aggregate" and "fillers" as used in the specification and theappended claims include both inorganic and inert organic particles butdo not typically include fibers. The term "inert organic particles" isfurther defined to include organic components that are not intended toprimarily chemically or mechanically act as a binding agent within themoldable mixture. Examples of inert organic particles include seeds,grains, cork, and plastic spheres. Although most aggregates within thescope of the present invention are insoluble in water, some aggregatesare slightly soluble in water, and some aggregates can be formed in situby precipitation or polymerization. (However, many seeds contain starch,proteins, or other polymeric materials in high enough quantities thatthey may be released into the moldable mixture and impart a bindingforce within the mixture.)

Articles with a high filler or aggregate content can be made having alower cost, improved mechanical and structural properties, better healthsafety, and minimal environmental impact. Studies have found thatfunctional articles of the present invention can be made using fillersup to about 90% by volume.

From a materials cost stand point, it is more economical to replace therelatively expensive starch-based binder with a less expensiveaggregate. Typically, the density and weight of an article increase withincreased filler. As the density of the mixture increases, the volume ofmaterial used to make the article also increases. For example, holdingall other variables constant, a 40% increase in the concentration ofcalcium carbonate results in about a 30% savings in the consumption ofstarch-based binder. It is believed that as the percentage of fillerincreases, however, the ability of the cells within the starch-boundmatrix to expand is decreased, thereby increasing the density andrequiring more material to make the same article. Nevertheless, evenwith the increase in density, it may be more economical to producearticles having a higher filler content compared to those having arelatively low filler content.

Increasing the filler is also beneficial from a processing standpoint.Starch has a natural affinity for water (the most common solvent used).Accordingly, more energy is required to remove water from thestarch-based binder than from a filler. By increasing the fillercontent, there is less starch-based binder to absorb the water and lesswater is needed to gelate the starch-based binder. Furthermore, more ofthe water is absorbed by the filler. Accordingly, processing costs aredecreased by using high concentrations of filler, since less solvent andenergy is required to produce a form-stable article. Furthermore, theinorganic aggregate can also be used as a means for conducting heatquicker and more uniformly throughout the entire structural matrix. As aresult, form-stable articles can be made quicker and with a more uniformcross-section. The ability of the aggregate to conduct heat is, ofcourse, a function of the type of aggregate and can be selected by thoseskilled in the art.

By selecting an appropriate filler, the specific heat of the finalarticle can also be decreased. For example, articles made with calciumcarbonate were found to have a lower specific heat than those thatcontain only starch. As a result, such mires can be used for heating upfood or other items without significantly heating up the article. Forexample, the present articles can be used for heating up or cooking foodin an oven or microwave without destruction of the article. By selectingfillers with low specific heat, the articles of the present inventioncan be made having a specific heat in a preferred range from about 0.3J/g.K to about 2.0 J/g.K at a temperature of 20° C., with about 0.5J/g.K to about 1.5 J/g.K being more preferred, and about 0.7 J/g.K toabout 1.0 J/g.K being most preferred.

Increasing the filler content is also beneficial in varying the shape ofthe structural matrix of the article. As previously discussed, ifinsufficient moisture is removed from the mixture during formation ofthe article, the remaining solvent can cause the mixture to stick to themold and may also cause the article to crack or bubble. Likewise, thearticle can also crack if too much moisture is removed from the mixture.There is, therefore, a margin of time (dependent on variables such asthe heat of the molds and amount of solvent in the mixture) within whichthe articles should be removed from the heated molds to prevent crackingor sticking of the articles. This margin of time becomes narrower as theconcentration of starch-based binder within a moldable mixture isincreased. As the margin of time for removal of the article from themold decreases, it becomes more difficult to manufacture articles havingcross-sections of varying thicknesses.

That is, at times it may be preferred to increase the thickness at aspecific section of an article to increase properties such as strengthor insulation at that section. However, heating the mixture for asufficient period of time to remove the solvent from the thick sectionmay remove too much moisture from the thinner sections. Thus, mixtureshaving a high starch-based binder content are typically limited to themanufacture of articles having a more uniform cross-section.

In contrast, studies have found that as the percentage of inorganicsincreases and the percentage of starch-based binder decreases, themargin of time in which the articles can be removed form the moldswithout sticking or cracking increases. As a result, articles having ahigh concentration of inorganics can be used to more effectivelymanufacture articles having varying cross-section thickness. Articleshave been made in which the thickness of the article varies by a factorof three.

There are also health benefits to using higher concentrations of filler.Increasing the amount of aggregate or filler in a mixture decrease theamount of water needed to be absorbed by the article during theconditioning stage to obtain the desired properties. As previouslydiscussed, minimizing the amount of water in an article is preferredsince it minimizes the chance for bacterial growth. Studies have foundthat the more calcium carbonate in a mixture, the slower the moisture isabsorbed by the article in the conditioning stage. It was alsodiscovered that the more calcium carbonate in a mixture, the lessmoisture needed to be adsorbed by the article to produce the sameproperties. Accordingly, increasing the filler content decreases therequired moisture content in the final product, as well as thepropensity of the article to absorb even more water from the atmosphere.

By selecting the type of filler used, the properties of the filler canbe transferred to the finished article. The aggregate materials employedin the present invention can be added to increase the strength (tensilemodulus and, especially, compressive strength), increase the modulus ofelasticity and elongation, decrease the weight, and/or increase theinsulation ability of the resultant inorganically filled article. Inaddition, plate-like aggregates, such as mica and kaolin, can be used inorder to create a smoother surface finish in the articles of the presentinvention. Typically, larger aggregates, such as calcium carbonate, givea matte surface, while smaller particles give a glassy surface.

Finally, there are also environmental benefits to having a high fillercontent. Articles with high filler contents are more easily decomposedback into their natural components, thereby minimizing visual blight.Furthermore, minimizing the starch-based binder reduces the amount ofwater that is consumed in the growing of starch-bearing plants. Particlepacking is a preferred process that can be used to maximize the amountof inorganics within the mixture and thus optimize the above discussedproperties. Studies have found that the packing density of a mixture isincreased where two or more types of aggregate having a difference intheir average particle size diameter are used. Particle packing is theprocesses of selecting different sizes, shapes, and concentration of theaggregates to minimize the interstitial space between the particles andmaximize the packing density. By minimizing the interstitial space, lesssolvent and starch-based binder needs to be added to the mixture to fillthe interstitial space.

To form an article having a more form-stable, crack-free structuralmatrix, the starch-based binder must usually be added in an amountsufficient to bind the aggregate together. As previously discussed, themixture is prepared by combining an inorganic aggregate with a solventand starch-based binder. The solvent disperses the starch-based binderand controls the viscosity. During the formation process, a majority ofthe solvent is removed. The volume of solvent and starch-based binderthat remains within the final article must be sufficient to coat theaggregate particles and fill the interstitial voids between theparticles so that the starch-based binder can bind the aggregateparticles together.

If insufficient quantities of the starch-based binder are added, minutepores form between the aggregate particles. These minute pores aredifferent from the cells which are preferably designed within thestructural matrix. Whereas the cells result from the expansion of thesolvent during the processing step, the pores result from aninsufficient amount of starch-based binder to bind the aggregateparticles together. If the volume of starch-based binder is furtherdecreased, the volume of the binder becomes so minute that either thestructural matrix will crack during the formation process or the mixturewill never consolidate into a form-stable article.

The ability of the starch-based binder to hold the aggregate particlestogether is a function of its intrinsic bond strength, coveting power,and its ability to bond with the surface of a particular material. Inthe manufacture of articles in which a binder matrix holds together avery large concentration of matter, the binder preferably envelops eachof the matter particles. If the matter to be held together has arelatively high surface area, then the amount of binder required toenvelop the matter particles increases. That is, the ratio of binder tomatter increases as the specific surface area of the matter increases.In the present invention, it is often preferable to select an aggregatematerial having lower specific surface area in order to reduce thebinder to matter ratio. In addition, as explained more fully below,increasing the particle packing density of the aggregate material alsodecreases the amount of binder needed to fully envelop the aggregateparticles. An understanding of the interaction between particle sizedistribution, the particle packing density, specific surface area, andbinder volume is at the core of the successful loading of relativelyhigh levels of inorganic solids within the starch-bound matrix.

In addition to specific surface area, the volume of starch-based binderrequired is related to the volume of interstitial space between theparticles. The volume of interstitial space increases in a mixture aseither the packing density of the aggregate decreases or the percentageof the aggregate in the mixture increases. Accordingly, by holding theconcentration of starch-based binder and aggregate constant by weight ofthe solids within a mixture and decreasing the packing density of theaggregate, the interstitial space will increase to a point in which thevolume of starch-based binder is insufficient to adequately fill theinterstitial space. Likewise, by adding a higher concentration ofaggregates, although the percentage of interstitial space remainsrelatively constant, the total volume of interstitial space increases.As a result, more starch-based binder must be added to the mixture toadequately fill the spaces. As more starch-based binder is added,however, the concentration of inorganics decreases in the finalarticles, thereby increasing the cost and minimizing the above discussedbenefits.

In contrast, as the packing density of the aggregate increases, theinterstitial space between the particles decreases. As a result, lessstarch-based binder and solvent are needed to fill the interstitialspace. By decreasing the amount of starch-based binder to only theminimum amount needed to bind the aggregate particles and impart thedesired physical properties, the percentage of inorganics in the finalarticles may be increased without sacrificing the desired strength andrheological properties. As such, the cost of the articles is decreasedand the above discussed properties are enhanced.

The volume of starch-based binder required is also dependent on the sizeand shape of the aggregate. Aggregates having a large specific surfacearea compared to aggregates of equal volume having a small specificsurface area require more starch-based binder to coat the particles.Coating the aggregate with the gelated starch-based binder is necessaryto bind the aggregate together. In addition, the greater specificsurface area utilizes more of the available water within the mixture inthe coating of the particle surfaces, resulting in less water beingavailable to react with and gelate the starch.

Accordingly, in order to maximize the inorganics and minimize the volumeof starch-based binder, it is preferable for the aggregates to have asmaller specific surface area. The highly inorganically filled articlesof the present invention preferably employ aggregates having a specificsurface area in a range from about 0.1 m² /g to about 400 m² /g, withabout 0.15 m² /g to about 50 m² /g being more preferred, and about 0.2m² /g to about 2.0 m² /g being most preferred. Particles having arelatively small specific surface area typically have a large averagediameter and are spherical in shape.

For a mixture to obtain the desired viscosity to form an article, thesolvent must be added in an amount sufficient to coat all of theparticles and fill all remaining interstitial space between theparticles. The interstitial space relevant to the solvent include thespaces between the aggregates and also between the any remainingungelated starch granules. Even with the interstitial space filled withsolvent, however, the mixture still may have a relatively highviscosity. To obtain a desired lower viscosity, an additional amount ofsolvent must be added to the mixture. That is, it is the amount ofsolvent added beyond what is necessary to coat the particles and fillthe interstitial space that actually provides the lubrication betweenthe surfaces of the particles.

The following illustrates how increasing the packing density decreasesthe amount of solvent and starch-based binder needed to fill theinterstitial space. If the particle packing density of the moldablemixture is 0.65, a solvent will be included in an amount of roughly 35%by volume in order to substantially fill the interstitial voids betweenthe particles. On the other hand, a moldable mixture having aparticle-packing density of 0.95 will only require solvent in an amountof about 5% by volume in order to substantially fill the interstitialvoids. This is a seven-fold decrease in the amount of solvent which mustbe added in order to substantially fill the interstitial voids. Reducingthe amount of solvent that would otherwise be required to fill theinterstitial space permits the articles to be made more quickly and witha lower energy consumption.

In order to optimize the packing density, differently sized aggregateswith particle sizes ranging from as small as about 0.05 μm to as largeas about 2 mm may be used. To maximize the strength of the cell walls,it is preferred that the particles not be greater then 1/4 the thicknessof the cell walls. Spherical particles having minimal fractured surfacesare preferred since they can be packed to a higher density and have thelowest specific surface area. In order to obtain an optimized level ofparticle packing, it is preferable for the average particle size withinone size range to be roughly 10 times the particle size of the nextsmallest particle range. (In many cases, the ratio will differ and isdependent on the relative natural packing densities of the differentaggregates to be combined.) For example, in a two-component system, itwill be preferable for the average particle size of the coarse componentto be at about 10 times the average particle size of the fine component.Likewise, in a three-component system, it will be preferable for theaverage particle size of the coarse component to be about 10 times theaverage particle size of the medium component, which will likewisepreferably be about 10 times the size of the fine component.Nevertheless, as more differently sized particles are added, the ratiobetween the particle size magnitudes need not always be this great andmay only be two-fold in some cases.

In general, a two-component (or binary) packing system will seldom havean overall packing density higher than about 80%, while the upper limitfor a three-component (or ternary) system is about 90%. To obtain higherparticle packing it will be necessary in most cases to add four or morecomponents, although having broader and more optimized particle sizesamong two- or three-component systems can yield higher overall particlepacking than 80% and 90%, respectively.

For example, in a three-component system, it has been found preferablefor the fine aggregate particles to have diameters in a range from about0.01 μm to about 2 μm, for the medium aggregate particle to havediameters in a range from about 1 μm to about 20 μm, and for the coarseaggregates to have a diameter in a range from about 100 μm to about 2mm. In a two component system, any two of these ranges may bepreferable.

Improved packing densities for the aggregate can be obtained byphysically combining different sizes and amounts of aggregates and thenusing conventional testing methods to determine the combination ofaggregates that has the highest packing density. In light of thepossible permutations, however, such a process is very time consumingand does not necessarily provide the best results. In the preferredembodiment, the aggregates are selected to obtain a desired packingdensity based on the particle packing process as disclosed in thefollowing article coauthored by one of the inventors of the presentinvention: Johansen, V. & Andersen, P. J., "Particle Packing andConcrete Properties," Materials Science of Concrete II at 111-147, TheAmerican Ceramic Society (1991). Further information is available in theDoctoral Dissertation of Anderson, P. J., "Control and Monitoring ofConcrete Production--A Study of Particle Packing and Rheology," TheDanish Academy of Technical Sciences. The preferred process of particlepacking is also discussed in detail in U.S. patent application Ser. No.08/109,100, now abandoned, entitled "Design Optimized Compositions andProcesses for Microstructurally Engineering Cementitious Mixtures", toPer Just Andersen and Simon K. Hodson, filed on Aug. 18, 1993. Forpurposes of disclosure, the foregoing article, doctoral dissertation,and patent application are incorporated herein by specific reference.

The above references teach the use of mathematical models to determinethe combination of defined groups of particles that will result in themaximum packing density. The models are based on the average diametersize and natural packing density for each type of aggregate. In general,the combined particle packing density for the aggregate mixture willpreferably be in a range from about 0.65 to about 0.99, more preferablyfrom about 0.70 and about 0.95, and most preferably from about 0.75 andabout 0.90. (The added cost of achieving 99% particle packing efficiencyis often prohibitive; therefore, most preferred packing densities aresomewhat less).

There are a variety of types of aggregates that can be used in thepresent invention. Inorganic materials commonly used in the paperindustry, as well as more finely ground aggregate materials used in theconcrete industry, may be used in the moldable mixtures of the presentinvention. The size of the aggregate or inorganic filler will usually bemany times greater than the inorganic filler materials typically used inthe paper industry.

Examples of useful aggregates include perlite, vermiculite, sand,gravel, rock, limestone, sandstone, glass beads, aerogel, xerogels,seagel, mica, clay, synthetic clay, alumina, silica, fly ash, fusedsilica, tabular alumina, kaolin, microspheres, hollow glass spheres,porous ceramic spheres, gypsum (calcium sulfate dihydrate), calciumcarbonate, calcium aluminate, lightweight polymers, xonotlite (acrystalline calcium silicate gel), lightweight expanded clays, hydratedor unhydrated hydraulic cement particles, pumice, exfoliated rock, andother geologic materials. Partially hydrated and hydrated cement, aswell as silica fume, have a high surface area and give excellentbenefits such as high initial cohesiveness of the freshly formedarticle. Even discarded inorganically filled materials, such asdiscarded containers or other articles of the present invention can beemployed as aggregate fillers and strengtheners. It will also beappreciated that the containers and other articles of the presentinvention can be easily and effectively recycled by simply adding themto fresh moldable mixtures as an aggregate filler. Hydraulic cement canalso be added in either its hydrated or unhydrated form.

Both clay and gypsum are particularly important aggregate materialsbecause of their ready availability, extreme low cost, workability, easeof formation, and because they can also provide a degree of binding andstrength if added in high enough amounts (in the case of gypsumhemihydrate). Because gypsum hemihydrate can react with the water withinthe moldable mixture, it can be employed as a means for holding waterinternally within the molded article.

In some cases, it may be desirable to form ettringite on the surface ofthe aggregate particles in order to improve the interaction and bondinterface between the aggregate particles and the starch-based binder.

Because of the nature of the moldable mixtures and articles madetherefrom, it is possible to include lightweight aggregates having ahigh amount of interstitial space in order to impart an insulationeffect with the molded articles. Examples of aggregates which can add alightweight characteristic and higher insulation to the molded articlesinclude perlite, vermiculite, glass beads, hollow glass spheres,synthetic materials (e.g., porous ceramic spheres, tabular alumina,etc.), cork, pumice, and lightweight expanded clays, sand, gravel, rock,limestone, sandstone, and other geological materials.

Porous aggregates can also be used to remove unwanted air bubbles fromthe article during formation. Solvents escape from the moldable mixtureby first traveling to the surface of the molds and then traveling alongthe mold surface to the vent holes. At times, air bubbles get trappedbetween the male mold and the outside surface of the article, therebypocking the surface. A porous aggregate within the moldable mixture canbe used to absorb a significant portion of this entrapped gas, therebyhelping to reduce the incidence of pocking. Of course, the entrapped gasbubbles can be removed through the application of a vacuum.

Porous, lightweight aggregates, including zeolites, can be used as ameans for conditioning the article during the forming process. Porousaggregates can be presoaked in a solvent or held in the mixture for asufficient period of time to absorb the solvent. As the mixturecontaining the presoaked aggregate is heated to form the article, thesolvent is released more slowly from within the porous aggregate thanfrom the remainder of the mixture. As a result, a portion of the solventwill remain within the porous aggregate in the form-stable article. Oncethe article is formed and removed from the heated molds, the solventwithin the porous aggregate can diffuse into the surrounding structuralmatrix, thereby conditioning and softening the structural matrix.

In addition to conventional aggregates used in the paper and cementindustries, a wide variety of other aggregates, including metals andmetal alloys (such as stainless steel, iron, copper, silver, and gold),balls or hollow spherical materials (such as glass, polymeric, andmetals), filings, and pellets can be added to the mixture.

Another class of aggregates that may be added to the inorganicallyfilled mixture includes gels and microgels such as silica gel, calciumsilicate gel, aluminum silicate gel, and the like. These can be added insolid form as any ordinary aggregate material might, or they may beprecipitated in situ. Because they tend to absorb solvents, they can beadded to reduce the solvents content (which will increase the viscosityand yield stress) of the moldable mixture.

In addition, the highly hygroscopic nature of silica-based gels andmicrogels allows them to be used as moisture regulation agents withinthe final hardened article. By absorbing moisture from the air, the gelsand microgels will cause the articles to retain a predetermined amountof moisture under normal ambient conditions. (Of course, the rate ofmoisture absorption from the air will correlate with the relativehumidity of the air). Controlling the moisture content of the articlesallows for more careful control of the elongation, modulus ofelasticity, bendability, foldability, flexibility, and ductility of thearticles. Other moisture retention admixtures, such a MgCl₂, arediscussed more fully below.

It is also within the scope of the present invention to includepolymerizable inorganic aggregate materials, such as polymerizablesilicates, within the moldable mixture. These may be added to themixture as ordinary silica or silicates, which are then treated to causea polymerization reaction in situ in order to create the polymerizedsilicate aggregate. Polymerized inorganic aggregates are oftenadvantageous in certain applications because of their increasedflexibility compared to most other inorganic aggregate materials.

The thermal conductivity or "k-factor" (defined as W/m.K) of the presentarticles can be selected by controlling the cellular structural matrix.Articles can be made having a low k-factor by having a higherconcentration of cells within the structural matrix. In embodiments inwhich it is desirable to obtain a container or other article having aneven higher insulation capability, it may be preferable to incorporateinto the highly inorganically filled matrix a lightweight aggregatewhich has a low thermal conductivity. Generally, aggregates having avery low k-factor also contain large amounts of trapped interstitialspace, air, mixtures of gases, or a partial vacuum which also tends togreatly reduce the strength of such aggregates. Therefore, concerns forinsulation and strength tend to compete and should be carefully balancedwhen designing a particular mixture.

Preferred insulating, lightweight aggregates include expanded orexfoliated vermiculite, perlite, calcined diatomaceous earth, and hollowglass spheres--all of which tend to contain large amounts ofincorporated interstitial space. However, this list is in no wayintended to be exhaustive, these aggregates being chosen because oftheir low cost and ready availability. Nevertheless, any aggregate witha low k-factor, which is able to impart sufficient insulation propertiesto the container or other article, is within the scope of the presentinvention. In light of the foregoing, the amount of aggregate which canbe added to the moldable mixture depends on a variety of factors,including the quantity and types of other added components, as well asthe particle packing density of the aggregates themselves. Bycontrolling the cellular structure and the addition of lightweightaggregate, articles can be made having a preferred k-factor in a rangeof about 0.03 W/m.K to about 0.2 W/m.K. Insulating articles can have amore preferred k-factor in a range of about 0.04 W/m.K to about 0.06W/m.K. Non-insulating articles can have a more preferred k-factor in arange of about 0.1 W/m.K to about 0.2 W/m.K.

The inorganic aggregates will preferably be included in an amount in arange from about 20% to about 90% by weight of the total solids withinthe inorganically filled moldable mixture, more preferably in a rangefrom about 30% to about 70%, and most preferably in a range from about40% to about 60%. The inert organic aggregates will preferably beincluded in an amount in a range from about 5% to about 60% by weight ofthe total solids, more preferably in a range from about 15% to about50%, and most preferably in a range from about 25% to about 40% byweight. Lightweight aggregates, defined as those having a density lowerthan about 1 g/cm³, are preferably included in an amount in a range fromabout 5% to about 85% by volume of the inorganically filled moldablemixture, more preferably in a range from about 15% to about 65%, andmost preferably in a range from about 25% to about 55% by volume.

As set forth above, differently sized aggregate materials may be addedin varying amounts in order to affect the particle-packing density ofthe moldable mixture. Depending upon the natural packing density of eachaggregate material, as well as the relative sizes of the particles, itis possible that the resulting volume of the combined aggregates will beless than the sum of the volumes of the aggregates before they weremixed.

D. Mold-Releasing Agents

To assist in removing the form-stable article from the molds, amold-releasing agent can be added to the moldable mixture. A preferredmold-releasing agent is magnesium stearate. Magnesium stearate functionsas a lubricant and emulsifier and is well known as an anti-caking agentthat is insoluble in water. On a more general scale, medium- andlong-chain fatty acids, their salts, and their acid derivatives can beused as mold-releasing agents. The preferred medium and long chain fattyacids typically occur in the production of vegetable and animal fats andhave a carbon chain greater than C₁₂. The most preferred fatty acidshave a carbon chain length from C₁₆ to C₁₈. The fats and salts usedherein need not be in a pure form but merely need to be the predominantcomponent. That is, the shorter or longer chain length fatty acids, aswell as the corresponding unsaturated fatty acids, can still be present.

Various waxes, such as paraffin and bees wax, and Teflon-based materialscan also be used as a mold releasing agent. One of the added benefits ofusing wax is that it can also act as a coating material, as discussedlater. Other materials, such as CaS, calcium silicate and Lecithin, havebeen found to work as mold releasing agents. To further assist inreleasing the articles from the molds, the molds can be polished, chromeplated, or coated with, e.g., nickel, Teflon, or any other material thatlimits the tendency of the article to stick to the molds.

The above mold releasing agents are preferably added to the mixture in arange from about 0.05% to about 15% by weight of the total solids, morepreferably in a range from about 0.1% to about 10%, and most preferredin a range from about 0.5% to about 5%.

E. Fibers

As used in the specification and the appended claims, the terms "fibers"and "fibrous materials" include both inorganic fibers and organicfibers. Fibers have successfully been incorporated into brittlematerials, such as ceramics, to increase the cohesion, elongationability, deflection ability, toughness, fracture energy, and flexural,tensile, and, on occasion, compressive strengths of the material. Ingeneral, fibrous materials reduce the likelihood that the highlyinorganically filled containers or other articles will shatter whencross-sectional forces are applied. Although fibers have been founduseful in increasing these properties in the articles of the presentinvention, their success has been limited.

As was previously discussed, the formed articles of the presentinvention have a foamed or cellular structural matrix. As a result,there is a limited amount of interfacial surface area for load transferbetween the fibers and structural matrix. That is, the fibers areconnected to the structural matrix of the formed articles only by thewalls dividing the cells. The remainder of the fiber is suspended in thecell. In some cases, the fibers are small enough to reside within thecell. As a result of the minimal contact between the fibers and thestructural matrix of the article, only a limited portion of theproperties of the fibers are incorporated into the structure matrix.

Fibers which may be incorporated into the inorganically filled matrixpreferably include naturally occurring organic fibers, such ascellulosic fibers extracted from hemp, cotton, plant leaves, sisal,abaca, bagasse, wood (both hard wood or soft wood, examples of whichinclude southern hardwood and southern pine, respectively), or stems, orinorganic fibers made from glass, graphite, silica, ceramic, or metalmaterials.

Recycled paper fibers can be used, but they are somewhat less desirablebecause of the fiber disruption that occurs during the original papermanufacturing process. Any equivalent fiber, however, which impartsstrength and flexibility is also within the scope of the presentinvention. The only limiting criteria is that the fibers impart thedesired properties without adversely reacting with the otherconstituents of the inorganically material and without contaminating thematerials (such as food) stored or dispensed in articles made from thematerial containing such fibers. For purposes of illustration, sisalfibers are available from International Filler, abaca fibers areavailable from Isarog Inc. in the Philippines, while glass fibers, suchas Cemfill®, are available from Pilkington Corp. in England.

Studies have found that fibers having a relatively higher diameter orwidth are more effective in increasing the energy to failure and thedisplacement to failure. For example, sisal fibers having an averagediameter of about 100 μm were far more effective in increasing the aboveproperties then the wood fibers having an average diameter of 10 μm. Theaddition of the sisal fibers also dramatically decreased the stiffnessin the dry cups.

Larger diameter fibers result in less surface area than small diameterfibers of equal volume. As the exposed surface area of the fiberdecreases, less solvent is adsorbed by the fibers, and, accordingly, thesolvent is removed quicker with less energy. The fibers used in thepresent invention preferably have an average diameter in a range fromabout 10 μm to about 100 μm, with about 50 μm to about 100 μm being morepreferred, and about 75 μm to about 100 μm being most preferred.Furthermore, the fibers should have an average aspect ratio(length-to-width ratio) of at least about 10:1.

The amount of fibers added to the moldable mixture will vary dependingupon the desired properties of the final product. The flexural strength,roughness, flexibility, and cost are the principle criteria fordetermining the amount of fiber to be added in any mix design. Theconcentration of fibers within the final hardened article willpreferably be in the range from about 0.5% to about 60% by volume of thetotal solids content, more preferably from about 2% to about 40%, andmost preferably from about 5% to about 20%.

Fiber strength is a consideration in determining the amount of the fiberto be used. The greater the flexural strength of the fiber, the less theamount of fiber that must be used to obtain a given flexural strength inthe resulting article. Of course, while some fibers have a highflexural, tear and burst strength, other types of fibers with a lowerflexural strength may be more elastic. A combination of two or morefibers may be desirable in order to obtain a resulting product thatmaximized multiple characteristics, such as higher flexural strength,higher elasticity, or better fiber placement.

It should also be understood that some fibers, such as southern pine andabaca, have high tear and burst strengths, while others, such as cotton,have lower strength but greater flexibility. In the case where betterplacement, higher flexibility, and higher tear and burst strength aredesired, a combination of fibers having varying aspect ratios andstrength properties can be added to the mixture.

It is known that certain fibers and inorganic fillers are able tochemically interact with and bind with certain starch-based organicpolymer binders, thereby adding another dimension to the materials ofthe present invention. For example, it is known that many fibers andinorganic fillers are anionic in nature and have a negative charge.Therefore, in order to maximize the interaction between the organicbinder and the anionic fibers and inorganic materials, it may beadvantageous to add a positively charged organic binder, such as acationic starch.

Better water resistance can be obtained by treating the fibers withrosin and alum (Al₂ (SO₄)₃) or NaAl(SO₄)₂, the latter of whichprecipitate out the rosin onto the fiber surface, making it highlyhydrophobic. The aluminum floc that is formed by the alum creates ananionic adsorption site on the fiber surface for a positively chargedorganic binder, such as a cationic starch.

Finally, the fibers may be coated with a variety of substances in orderto improve the desired properties of the final product. For example, thefibers may be coated in order to make them more resistant to waterabsorption. In addition, ettringite can be formed on the surface of thefibers in order to improve the interaction or interface between thefibers and the starch-based binder.

F. Rheology-Modifying Agents

Rheology-modifying agents act to increase the viscosity or cohesivenature of the moldable mixture. As previously discussed, increasing theviscosity decreases the size of the cells and increases the size of thecell walls within the structural matrix. The resulting article is thusdenser and has a higher strength. Increasing the viscosity is also usedto prevent settling of the aggregates and starch-based binder within themixture. Aggregates and ungelated starch granules have a naturaltendency to settle in low viscosity mixtures. As a result, during thetime period between the preparation and heating of the mixture to thepoint of gelation, the aggregate and any ungelated starch granules maybegin to settle, thereby producing an article having non-uniformproperties. Depending on the density of the aggregate, one of ordinaryskill in the art can select the type and amount of rheology-modifyingagent to be added to the mixture to prevent settling.

A variety of natural and synthetic organic rheology-modifying agents maybe used which have a wide range of properties, including viscosity andsolubility in water. The various rheology-modifying agents contemplatedby the present invention can be roughly organized into the followingcategories: (1) cellulose-based materials and derivatives thereof, (2)proteins and derivatives thereof, and (3) synthetic organic materials.

Suitable cellulose-based rheology-modifying agents include, for example,methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose,hydroxypropylmethylcellulose, etc. The entire range of possiblepermutations is enormous and shall not be listed here, but othercellulose materials which have the same or similar properties as thesewould also work well.

Other natural polysaccharide-based rheology-modifying agents include,for example, alginic acid, phycocolloids, agar, gum arabic, guar gum,locust bean gum, gum karaya, and gum tragacanth. Suitable protein-basedrheology-modifying agents include, for example, Zein® (a prolaminederived from corn), collagen (derivatives extracted from animalconnective tissue such as gelatin and glue), and casein (the principleprotein in cow's milk).

Finally, suitable synthetic organic rheology-modifying agents that arewater dispersable include, for example, polyvinyl pyrrolidone,polyethylene glycol, polyvinyl alcohol, polyvinylmethyl ether,polyacrylic acids, polyacrylic acid salts, polyvinyl acrylic acids,polyvinyl acrylic acid salts, polyacrylamides, ethylene oxide polymers,polylactic acid, and latex (which is a broad category that includes avariety of polymerizable substances formed in a water emulsion; anexample is styrene-butadiene copolymer). Synthetic organic polymers,especially the polyvinyl compounds, are also used as film binders toproduce a hydrophobic surface on the starch-based binder. Thehydrophobic surface slows down the rate of water absorption by thestarch-based binder in the mixing process, thereby permitting quickerformation of form-stable articles.

Rheology-modifying agents within the moldable mixtures of the presentinvention are preferably included in an amount such that a hardenedarticle will contain from about 0.5% to about 20% rheology-modifyingagent by weight of article, more preferably from about 1% to about 10%,and most preferably from about 2% to about 5%.

G. Dispersants

The term "dispersant" shall refer in the specification and the appendedclaims to the class of materials which can be added to reduce theviscosity and yield stress of the moldable mixture. A more detaileddescription of the use of dispersants may be found in the Master'sThesis of Andersen, P. J., "Effects of Organic SuperplasticizingAdmixtures and their Components on Zeta Potential and Related Propertiesof Cement Materials" (The Pennsylvania State University MaterialsResearch Laboratory, 1987). For purposes of disclosure, the foregoingMaster's Thesis is incorporated herein by specific reference.

Dispersants generally work by being adsorbed onto the surface of theaggregate particles and/or into the near colloid double layer of theparticles. This creates a negative charge on or around the surfaces ofthe particles causing them to repel each other. This repulsion of theparticles adds "lubrication" by reducing the friction or attractiveforces that would otherwise cause the particles to have greaterinteraction. This increases the packing density of the material somewhatand allows for the addition of less solvent while maintaining theworkability of the moldable mixture. Dispersants can be used to createlow viscosity, workable mixtures having a low concentration of solvent.Such mixtures are suited for the production of high density articles.

Due to the nature of the coating mechanism of the dispersant, the orderin which the dispersant is added to the mixture can often be important.If certain water-dispersible organic polymer rheology-modifying agents(such as Tylose®) are used, the dispersant should be added to a mixturecontaining water and at least part of the inorganic aggregates first andthen the rheology-modifying agents should be added second. Otherwise,the dispersant will be less able to become adsorbed onto the surface ofthe aggregate particles because the Tylose® will first be irreversiblyadsorbed, thereby forming a protective colloid on the surface andthereby preventing the dispersant from being adsorbed.

A preferred dispersant is polyacrylic acid. Another dispersant which canalso work well is meta phosphate. The amount of added dispersant willgenerally range up to about 5% by weight of the solvent, more preferablyin the range from about 0.5% to about 4%, and most preferably within therange from about 1% to about 2%.

The dispersants contemplated within the present invention have sometimesbeen referred to in the concrete industry as "superplasticizers." Inorder to better distinguish dispersants from other rheology-modifyingagents, which often act as plasticizers, the term "superplasticizer"will not be used in this specification.

H. Other Admixtures

A variety of other components can be added to the moldable mixture toimpart desired properties to the final article. For example, enzymessuch as carbohydrase, amylase, and oxidase produce holes in the surfaceof starch granules permitting the starch-based binder to gelate fasterin the case where ungelated starch is used. As a result, the viscosityof the mixture increases at a faster rate, thereby producing articleswith a stronger and more uniform cell structure.

Articles can initially be formed having a desired flexibility (asopposed to obtaining flexibility through the use of a humidity chamber)by adding components that will tightly bind the water within the starchmolecules. This can be achieved with the addition of humectants ordeliquescent chemicals, such as MgCl₂, CaCl₂, NaCl, or calcium citrate.Because all of these chemicals are readily water soluble, they are ableto distribute and retain water within the starch molecules to provide amore uniform distribution of moisture. In turn, the moisture improvesflexibility.

Flexibility can also be obtained by adding softeners or plasticizers tothe moldable mixture. Such plasticizers include Polysorbate 60, SMG,mono and diglycerides and distilled monoglycerides. Other specializedplasticizers having a boiling point above the maximum temperaturereached by the mixture during the forming process can also be used.These chemicals, which include polyethylene glycol (below 600 MW),glycerin, and sorbitol, tend to take the place of water and function asplasticizers with moisture as low as 5%. They are believed to attachthemselves to the hydroxyl groups of starch molecules and form ahinge-like structure. Since the plasticizers do not vaporize during theforming process, they remain within the form-stable article, therebysoftening the starch-bound matrix.

Finally, cross-linking admixtures such as dialdehydes, methylureas, andmelamine formaldehyde resins can be added to the mixture to produce aless water soluble starch-based binder. The cross-linking admixturesbind to the hydroxyl ions of the starch-based binder, which slow downthe water reabsorption rate of the starch-based binder. As a result, thefinal articles obtain form stability at a faster rate, have higherstrength, and are able to retain liquids longer before failure (e.g., acup can hold water longer before it starts to leak).

The above-listed admixtures are typically added in a range between about0.5% to about 15% by weight of the total solids in the mixture, orpreferably about 1% to about 10%, and more preferably from about 1% toabout 5%.

V. Processing Apparatus, Conditions, and Results

The articles of manufacture of the present invention are producedthrough a multi-step process. The steps include preparing the mixture,forming the mixture into the desired articles, and conditioning theresulting articles. Additional steps can selectively include theprinting, coating, and packaging of the final articles. The apparatusused in the processing steps are discussed below. The inventive articlescan be prepared using conventional equipment well known to those skilledin the arts of polystyrene foam, paper, plastic, cement, and ediblewafers. The equipment, however, must be uniquely combined and arrangedto form a functional system that can manufacture the present articles.Furthermore, slight modification of the equipment may be required tooptimize production of the articles. The arrangement, modification, andoperation of the equipment needed to manufacture the inventive articlescan be performed by those skilled in the art of using the conventionalequipment in light of the present disclosure.

A. Preparing the Mixture

As depicted in FIG. 4, the moldable mixture is preferably prepared in amixing tank 20 fed by bulk storage cells 22. The number of storage cells22 is dependent on the number of components to be incorporated into themixture. Storage cells 22 typically comprise dry load cells 24 andliquid load cells 26. Dry load cells 24 house solid components such asthe starch-based binder, fillers, and fibers. Dry material meteringunits 28, typically consisting of some form of auguring system,automatically and accurately measure and feed the desired amount of drymixture into mixing tank 20.

Liquid load cells 26 house liquid components such as the solvent anddifferent liquid rheology-modifying agents. When appropriate, automaticstirrers can be positioned within the liquid load cells 26 to helpprevent separation or settling of a liquid. Metering pumps 30automatically and accurately measure and feed the liquids into mixingtank 20.

Mixing tank 20 is preferably a high energy mixer capable of quicklyblending the components into a homogenous, moldable mixture. Such highenergy mixers include the TMN turbo batter mixers that are availablefrom Franz Haas Waffelmaschinen of Vienna, Austria. Alternative highenergy mixers are disclosed and claimed in U.S. Pat. No. 4,225,247entitled "Mixing and Agitating Device"; U.S. Pat. No. 4,552,463 entitled"Method and Apparatus for Producing a Colloidal Mixture"; U.S. Pat. No.4,889,428 entitled "Rotary Mill"; U.S. Pat. No. 4,944,595 entitled"Apparatus for Producing Cement Building Materials"; and U.S. Pat. No.5,061,319 entitled "Process for Producing Cement Building Material". Forpurposes of disclosure, the foregoing patents are incorporated herein byspecific reference.

Alternatively, a variable speed mixer can be used to provide low energymixing. Variable speed mixers include the Eirich Rv-11. Where fragilefillers or aggregates, such as glass spheres, are being incorporatedinto a mixture, it is preferred to use low energy mixing so as not tocrush the aggregate. Low energy mixing is more important for highviscosity mixtures. As the viscosity increases, the shear force appliedto the mixture increases, thereby increasing the damage to the fragileaggregates.

As further depicted in FIG. 4, once the mixture is prepared, it ispumped through an oscillating screen 32 to a storage mixer 34.Oscillating screen 32 helps to separate out and disperse unmixed clumpsof the solids. Storage mixer 34 functions as a holding tank to permitcontinuous feeding of the moldable mixture to the forming apparatus. Themoldable mixture is fed to the forming apparatus via a conventional pump36.

In one embodiment, storage mixer 34 is sealed closed and a vacuum pump38 is attached thereto. Vacuum pump 38 applies a negative pressure tothe mixture to remove air bubbles entrained in the mixture. Aspreviously discussed, air bubbles can cause surface defects within thefinal products.

Storage mixer 34 continuously stirs or mixes the moldable mixture at lowenergy to prevent settling within the moldable mixture. Where theforming apparatus operates on batch processing, as opposed to continuousprocessing, storage tank 34 can be eliminated and the mixture feddirectly from mixing tank 20 to the forming apparatus.

Where a thicker or more viscous moldable mixture is desired, it may benecessary to use an auguring system to mix and transfer the moldablemixture. In one embodiment, the materials incorporated into the moldablemixture are automatically and continuously metered, mixed, and deairedby a dual chamber auger extruder apparatus. FIG. 5 depicts a dualchamber auger extruder 40, which includes a feeder 42 that feeds themoldable mixture into a first interior chamber 44 of extruder 40. Withinfirst interior chamber 44 is a first auger screw 46 which both mixes andexerts forward pressure advancing the moldable mixture through firstinterior chamber 44 toward an evacuation chamber 48. Typically, anegative pressure or vacuum is applied to evacuation chamber 48 in orderto remove unwanted air voids within the moldable mixture.

Thereafter, the moldable mixture is fed into a second interior chamber50. A second auger screw 52 advances the mixture toward the articleforming apparatus. Auger screws 46 and 52 can have different flightpitches and orientations to assist in advancement of the mixture andperforming low and high shear energy mixing.

Auger extruder 40 can be used to independently mix the components forthe moldable mixture, or, as shown in FIG. 5, can be fed by a mixer 54.A preferable twin auger extruder apparatus utilizes a pair of uniformrotational augers wherein the augers rotate in the same direction.Counter-rotational twin auger extruders, wherein the augers rotate inthe opposite directions, accomplish the same purposes. A pugmil may alsobe utilized for the same purposes. Equipment meeting thesespecifications are available from Buhler-Miag, Inc., located inMinneapolis, Minn.

High viscosity, moldable mixtures are typically fed into the formingapparatus by either a two-stage injector or a reciprocating screwinjector. As depicted in FIG. 6, a two-stage injector 56 has separatecompartments for mixing or advancing and injecting. The mixture isconveyed to an extruder screw 58, which feeds the mixture to a shootingpot 60. Once shooting pot 60 is filled, an injection piston 62 pushes adefined quantity of the mixture into a flow channel 64 that feeds theforming apparatus.

As depicted in FIG. 7, a reciprocating screw injector 66 comprises achamber 68 having a screw auger 70 longitudinally positioned therein.The moldable mixture is fed into chamber 68 and advanced by screw auger70. As screw auger 70 rotates, it retracts and feeds the mixture toinjection end 72 of screw auger 70. When the required volume of themixture has accumulated at end 72, screw auger 70 stops rotating andmoves forward to inject the mixture into flow channel 64 andsubsequently to the forming apparatus.

B. Forming the Mixture into the Desired Article

Once the mixture is prepared, it is preferably formed into the desiredshape of the article through the use of heated molds. FIG. 8 depicts aheated male mold 74 having a desired shape and a heated female mold 76having a complementary shape. Female mold 76 comprises a mold body 78having a flat mold face 80 with a receiving chamber 82 bored therein.Receiving chamber 82 has a mouth 84 through which it is accessed. Malemold 74 comprises an attachment plate 86, a die head 88 having a shapesubstantially complementary to the shape of receiving chamber 82, and aventing ring 90 extending between attachment plate 86 and die head 88.Venting ring 90 is slightly larger than mouth 84 of receiving chamber 82and contains a plurality of venting grooves 92 that are longitudinallyaligned with die head 88.

In the preferred embodiment, the molds are vertically aligned withfemale mold 76 being positioned below male mold 74. In this orientation,as shown in FIG. 9, receiving chamber 82 acts as a container forreceiving the moldable mixture from a filling spout 94. Once the mixtureis positioned within female mold 76, the molds are mated, as shown inFIG. 10, by inserting die head 88 into receiving chamber 82 until ventring 90 comes to rest on mold face 80 around mouth 84. Die head 88 isslightly smaller than receiving chamber 82 so that when the molds aremated, a mold area 96 exists between male mold 74 and female mold 76. Aspreviously discussed, the amount of moldable mixture positioned infemale mold 76 preferably only fills a portion of mold area 96.

In the mated position as shown in FIGS. 11 and 11 A, vent grooves 92communicate with mold area 96 to form vent holes 98. Furthermore, aventing gap 100 is formed between mold face 80 and attachment plate 86as a result of venting ring 90 resting on mold face 80. Duringoperation, the heated molds cause the moldable mixture to expand and dryinto a solid article according to the process and parameters aspreviously discussed. Excess material 102 and vapor is expelled frommold area 96 through vent holes 98 and into venting gap 100. Once themixture becomes form-stable in the desired shape of the article, malemold 74 and female mold 76 are separated. As depicted in FIG. 12, ascraper blade 103 can then be pressed along the length of mold face 80to remove excess material 102.

The molds can have a variety of shapes and sizes to form the desiredarticle. However, there are two general types of molds: dual molds andsplit molds. As shown in FIG. 13, dual mold 104 comprises a single malemold 74 and a single female mold 76. This type of mold is used formaking shallow articles, such as plates and lids, that are easilyremoved from the molds. Split molds 106, as shown in FIG. 14, comprise asingle male mold 74 and a female mold 76 that can be separated into moldhalves 108. Mold halves 108 are separated after the article is formed topermit easy removal of the article. Split molds 106 are used for theproduction of deep recessed articles such as cups and bowls that can bedifficult to remove from a mold.

One method for removing articles from the mold is by a suction nozzle110. As shown in FIG. 14, suction nozzle 110 has a head 112 with vacuumports 114 located thereon. Head 112 is designed to complementarily fitwithin the hardened article. Accordingly, by inserting head 112 into thearticle and applying a slight negative pressure through vacuum ports114, the article can be picked up and moved to a conveyor belt forsubsequent processing.

The molds are preferably made of metals such as steel, brass, andaluminum. Polished metals, including chrome and nickel, along withTeflon coatings, make it easier to remove the articles from the moldsand create a smoother finish. The material of the molds must be able towithstand the temperatures and pressures, as previously discussed,encountered during the manufacturing process.

The molds can be heated in a variety of ways. For example, externalheating elements, such as gas burners, infrared light, and electricalheating elements, can be attached or directed at the molds.Alternatively, heated liquids, such as oils or heated gases, such assteam, can be piped through the molds to heat them. Various types ofheating can also be used to vary the temperature of the molds along thelength of the molds in order to vary the properties of the hardenedmatrix within the molded article.. It is also possible to heat themixtures without heating the molds. For example, the molds can be madeout of ceramic and microwaves be applied to heat the mixture.

By varying the temperature and processing time it is possible to affectthe density, porosity, and thickness of the surface layer, or skin.Generally, in order to yield a molded article having a thinner but moredense surface layer, the molding temperature is lower, the molds havefewer vents, and the moldable mixture has a higher viscosity. Theviscosity of the mixture can be increased by adding a rheology-modifyingagent, such as Tylose®, including less water, or by using an aggregatematerial having a higher specific surface area.

C. Conditioning the Articles

If the resulting form-stable articles have insufficient flexibility fortheir intended use, they are transferred to a high humidity chamber. Aspreviously discussed, the humidity chamber provides an environment ofcontrolled temperature and humidity to permit rapid moisture absorptionby the form-stable articles. Increasing the moisture content in thearticles improves certain properties, such as the elasticity,displacement-before-failure, and flexibility.

The humidity chamber can be designed for either batch processing orcontinuous processing. In continuous processing, the humidity chambercomprises either a tunnel or tower through which the articles passwithout stopping. The length or height of the chamber, speed of theconveyor system, humidity within the chamber, and temperature within thechamber are optimized to produce an article having the desired moisturecontent in a minimum time period and minimum cost. Preferred variablesfor moisture content, humidity level, and temperature are previouslydiscussed.

The moisture can be produced through conventional hot and cold steamprocesses as well as vaporization with ultrasound. Examples ofcommercially available humidity chambers that can be used in the presentinvention include the KTV, KT, and KTU wafer sheet conditioning tunnelsand towers available from Franz Haas Waffelmaschinen of Vienna, Austria.

D. Coatings and Coating Apparatus

It is within the scope of the present invention to apply coatings orcoating materials to the articles. Coatings can be used to alter thesurface characteristics of the articles in a number of ways, includingsealing and protecting the article. Coatings may provide protectionagainst moisture, base, acid, grease, and organic solvents. They mayalso fill in voids on the surface of the article and provide a smoother,glossier, or scuff-resistant surface. Furthermore, coatings can helpprevent aggregate and fiber "fly away". Coatings may also providereflective, electrically conductive or insulative properties. They mayeven reinforce the article, particularly at a bend, fold, edge orcorner. Some of the coatings can also be utilized as laminatingmaterials or as adhesives.

Application of a coating may also be used to regulate the moisturecontent of the present articles. It is theorized that the moisturecontent of an article will eventually reach a point of equilibrium withits environment. That is, relatively dry articles will adsorb moisturein a humid climate and conditioned articles will loose moisture in a dryclimate. The application of a coating after conditioning the article tothe proper moisture content can prevent the exchange of moisture betweenarticle and the surrounding environment.

The object of the coating process is usually to achieve a uniform filmwith minimal defects on the surface of the article. Selection of aparticular coating process depends on a number of substrate (i.e.,article) variables, as well as coating formulation variables. Thesubstrate variables include the strength, weltability, porosity,density, smoothness, and uniformity of the article. The coatingformulation variables include total solids content, solvent base,surface tension, and rheology.

The coating can be applied either during the forming process or afterthe article is formed. The coating can be formed during the formingprocess by adding a coating material that has approximately the samemelting temperature as the peak temperature of the mixture. As themixture is heated, the coating material melts and moves with thevaporized solvent to the surface of the article where it coats thesurface. Such coating materials include selected waxes and cross-linkingagents.

The coatings may be applied to the article after formation by using anycoating means known in the art of manufacturing paper, paperboardplastic, polystyrene, sheet metal, or other packaging materials,including blade, puddle, air-knife, printing, Dahlgren, gravure, andpowder coating. Coatings may also be applied by spraying the articlewith any of the coating materials listed below or by dipping the articleinto a vat containing an appropriate coating material. The apparatusused for coating will depend on the shape of the article. For example,cups will usually be coated differently than flat plates.

As the articles having a starch-based binder have a high affinity forwater, the preferred coatings are non-aqueous and have a low polarity.Appropriate coatings include paraffin (synthetic wax); shellac;xylene-formaldehyde resins condensed with4,4'-isopropylidenediphenolepichlorohydrin epoxy resins; drying oils;reconstituted oils from triglycerides or fatty acids from the dryingoils to form esters with various glycols (butylene gylcol, ethyleneglycol), sorbitol, and trimethylol ethane or propane; synthetic dryingoils including polybutadiene resin; natural fossil resins includingcopal (tropical tree resins, fossil and modern), damar, elemi, gilsonite(a black, shiny asphaltitc, soluble in turpentine), glycol ester ofdamar, copal, elemi, and sandarac (a brittle, faintly aromatictranslucent resin derived from the sandarac pine of Africa), shellac,Utah coal resin; rosins and rosin derivatives including rosin (gumrosin, tall oil rosin, and wood rosin), rosin esters formed by reactionwith specific glycols or alcohols, rosin esters formed by reactionformaldehydes, and rosin salts (calcium resinate and zinc resinate);phenolic resins formed by reaction of phenols with formaldehyde;polyester resins; epoxy resins, catalysts, and adjuncts;coumarone-indene resin; petroleum hydrocarbon resin (cyclopentadienetype); terpene resins; urea-formaldehyde resins and their curingcatalyst; triazine-formaldehyde resins and their curing catalyst;modifiers (for oils and alkyds, including polyesters); vinyl resinoussubstances (.polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol,etc.); cellulosic materials (carboxymethylcellulose, cellulose acetate,ethylhydroxyethylcellulose, etc.); styrene polymers; polyethylene andits copolymers; acrylics and their copolymers; methyl methacrylate;ethyl methacrylate; waxes (paraffin type I, paraffin type II,polyethylene, sperm oil, bees, and spermaceti); melamine; polyamides;polylactic acid; Biopol® (a polyhydroxybutyrate-hydroxyvaleratecopolymer); soybean protein; other synthetic polymers includingbiodegradable polymers; and elastomers and mixtures thereof. Biopol® ismanufactured by ICI in the United Kingdom. Appropriate inorganiccoatings include sodium silicate, calcium carbonate, aluminum oxide,silicon oxide, kaolin, day, ceramic and mixtures thereof. The inorganiccoatings may also be mixed with one or more of the organic coatings setforth above.

In some cases, it may be preferable for the coating to be elastomeric ordeformable. Some coatings may also be used to strengthen places wherethe articles are severely bent. In such cases, a pliable, possiblyelastomeric, coating may be preferred. A waterproof coating is desirablefor articles intended to be in contact with water. If the articles areintended to come into contact with foodstuffs, the coating material willpreferably comprise an FDA-approved coating.

Polymeric coatings such as polyethylene are useful in forming generallythin layers having low density. Low density polyethylene is especiallyuseful in creating containers which are liquid-tight and evenpressure-tight to a certain extent. Polymeric coatings can also beutilized as an adhesive when heat sealed.

Aluminum oxide and silicon oxide are useful coatings, particularly as abarrier to oxygen and moisture. The coatings can be applied to thearticle by any means known in the art, including the use of a highenergy electron beam evaporation process, chemical plasma deposition andsputtering. Mother method of forming an aluminum oxide or silicon oxidecoating involves the treating of the article with an aqueous solutionhaving an appropriate pH level to cause the formation of aluminum oxideor silicon oxide on the article due to the composition of the article.

Waxes and wax blends, particularly petroleum and synthetic waxes,provide a barrier to moisture, oxygen, and some organic liquids, such asgrease or oils. They also allow an article such as a container to beheat sealed, Petroleum waxes are a particularly useful group of waxes infood and beverage packaging and include paraffin waxes andmicrocrystalline waxes.

E. Printing

It may be desirable to apply print or other indicia, such as trademarks,product information, container specifications, or logos, on the surfaceof the article. This can be accomplished using any conventional printingmeans or processes known in the art of printing paper or cardboardproducts, including planographic, relief, intaglio, porous, andimpactless printing. Conventional printers include offset, Van Dam,laser, direct transfer contact, and thermographic printers. However,essentially any manual or mechanical means can be used.

The type of printing and printer used depends in part on the shape ofthe article. For example, flat plates will require a different printingapparatus than a cup. In addition, the molds can be specially designedto provide embossing on the surface of the article. The article can alsobe provided with a watermark. Because the articles have a relativelyhigh porosity, the applied ink will tend to dry rapidly. One skilled inthe art will appreciate that the article porosity and ink quantitiesmust be compatible. In addition, decals, labels or other indicia can beattached or adhered to the article using methods known in the art.

F. Packaging

A custom automatic stacker can be installed at the end of manufacturingline to create stacks of articles. The stacks are loaded into poly bagsand then sealed. Finally, standard carton handling/palletizing equipmentis used to package the articles and prepare them for shipping. Thepackaging equipment includes conventional equipment used in packagingarticles made from paper, plastic, polystyrene foam, or metal.

G. Physical Properties of the Articles

In view of the foregoing, it is possible, by using a microstructuralengineering approach, to obtain a wide variety of articles of varyingshapes, strengths, flexibilities, stiffness, insulation, and otherphysical properties. In general, the flexural strength of the articleswill preferably be in a range of about 0.5 MPa to about 8 MPa, morepreferably in a range from about 0.75 MPa to about 6 MPa, and mostpreferably in a range from about 1 MPa to about 4 MPa. The range ofstrain of the articles (i.e., the amount of strain before rupture),which will preferably be in a range from about 1% to about 15%, morepreferably from about 1% to about 10%, and most preferably from about 1%to about 5%. The specific strength of the articles will vary in a rangefrom about 2 MPa. cm³ /g to about 80 MPa. cm³ /g. The fracture energy ofthe articles will preferably be in a range from about 5 J/m² to about3000 J/m², more preferably from about 15 J/m² to about 1500 J/m², andmost preferably from about 25 J/m² to about 600 J/m².

VI. EXAMPLES OF THE PREFERRED EMBODIMENTS

Outlined below are a number of examples showing the manufacture ofarticles from the inorganically rifled, starch-bound, moldable mixturesof the present invention. The examples compare the properties of thearticles for varying compositions and processing conditions.

Examples 1-13

Drinking cups were formed from moldable mixtures containing differenttypes of inorganic aggregates to determine the effects of the differentaggregates. Each of the moldable mixtures had the following basic mixdesign measured by weight:

    ______________________________________                                        39.8%        Stalok 400 (modified potato starch)                              9.95%        inorganic aggregate                                              49.75%       water                                                            0.5%         magnesium stearate                                               ______________________________________                                    

Each moldable mixture was prepared in a small Hobart mixer. First, thedry ingredients (including the inorganic aggregate, starch, andmagnesium stearate) were completely mixed. Then the water was addedslowly while the dry materials were being mixed until a homogeneousmixture was obtained. The mixtures were extracted from the Hobart mixingbowl using a syringe. The weight of the moldable material used tomanufacture a cup for each mixture was determined by first weighing thesyringe containing the moldable mixture, expelling the contents of thesyringe into the molding apparatus, and then weighing the syringe.

The molding system included a male mold made out of tooled brass and afemale mold made out of tooled steel, the molds being configuredsubstantially according to FIG. 8. The molds were designed to produce 12oz. drinking cups having a smooth surface and a thickness of about 4 mm.The male mold contained four vent grooves that formed four vent holes.

The cups of Examples 1-13 were obtained by heating each selectedmoldable mixture between the molds at a temperature of about 200° C.Once the articles became significantly form-stable, they were removedfrom the molds and placed in an oven for about 1.5 hours at atemperature of 105° C. to remove the remaining moisture. The moisturewas removed so that subsequent testing of the cups would better reflectthe effects of the component as opposed to the effects of thestarch-based binder moisture content. It was assumed that the weightloss of the cup during drying in the oven was a loss of water. Themeasured weight loss was thus used to determine the moisture of cupsupon being removed from the mold. The cups were then sealed in plasticbags to maintain a constant humidity until the cups could be tested.

Summarized below is a list of the selected inorganic aggregates and theresulting properties of the cups formed from each of the mix designs:

    ______________________________________                                                                  Moisture      Thermal                                                 Cup     Out of Thermal                                                                              Resist.                                      Inorganic  Density Mold   Conduct.                                                                             (ft.sup.2 -h-°F./              Example                                                                              Aggregate  (g/cc)  (% W/W)                                                                              (W/m · K)                                                                   BTU-in)                               ______________________________________                                        1      Gama Sperse                                                                              0.190   3.0    0.046  3.15                                  2      Carbital 50                                                                              0.185   2.5    0.044  3.25                                  3      RO40       0.215   2.7    0.045  3.20                                  4      Mica 4k    0.205   2.6    0.048  3.10                                  5      Glass Bubbles                                                                            0.190   4.9    0.047  3.15                                         B38/4000                                                               6      Polymica 400                                                                             0.195   2.0    0.049  2.90                                  7      Aerosil R972                                                                             0.125   4.2    0.040  3.68                                  8      Aerosil 130                                                                              0.135   4.0    0.054  2.70                                  9      Aerosil 200                                                                              0.145   4.1    0.046  3.15                                  10     Aerosil 380                                                                              0.155   4.3    0.048  3.10                                  11     Cabosil EH5                                                                              0.140   2.8    0.041  3.60                                  12     Wollastonite                                                                             0.195   2.1    N/A    N/A                                   13     Sil-co-sil 0.200   2.1    N/A    N/A                                          Silica Sand                                                            ______________________________________                                    

    ______________________________________                                                                    Displace-                                                                             Peak Stiff-                                      Inorganic  Energy to ment to Load ness                                 Example                                                                              Aggregate  Failure (mJ)                                                                            Failure (%)                                                                           (N)  (N/m)                                ______________________________________                                        1      Gama Sperse                                                                              6.0       3.1     5.00 2.5                                  2      Carbital 50                                                                              9.0       3.5     5.10 2.7                                  3      RO40       7.0       3.1     5.05 2.6                                  4      Mica 4k    N/A       N/A     N/A  N/A                                  5      Glass Bubbles                                                                            9.5       3.2     5.20 3.4                                         B38/4000                                                               6      Polymica 400                                                                             10.0      2.7     5.15 2.4                                  7      Aerosil R972                                                                             7.0       4.0     4.95 1.9                                  8      Aerosil 130                                                                              7.0       3.5     4.90 1.8                                  9      Aerosil 200                                                                              9.0       3.5     5.00 2.1                                  10     Aerosil 380                                                                              6.0       3.1     4.95 2.2                                  11     Cabosil EH5                                                                              7.0       3.4     4.95 2.0                                  12     Wollastonite                                                                             8.5       3.1     5.10 2.9                                  13     Sil-co-sil 8.0       2.8     5.05 3.0                                         Silica Sand                                                            ______________________________________                                    

The properties analyzed include thermal properties and mechanicalproperties. The thermal properties include thermal conductance andthermal resistivity which were determined by a transient hot-wiremethod. Three measurements were recorded for the thermal conductivity ofthe side walls of the cups and the average value was reported.Mechanical properties were defined by developing a test that wouldsimulate the pinching between the thumb and the other four fingers thata cup might experience during use. The results served as a means tocompare cups produced from different compositions and under differentconditions. The strength and ductility were not easily quantifiable dueto the complex geometry. Instead the data is reported withoutnormalization to the cross-sectional area.

The cups were positioned on an inclined platform. The inclination wasadjusted so that the side edge of the cup was normal to the loadingdirection. The area below the top rim of the cup was chosen as the pointof load application. This resulted in the most reproducible results.Loads were applied to the cups at the rate of 15 mm/min. until a clearfailure was observed. The displacements and the corresponding loads wererecorded.

The test provided a qualitative evaluation of the mechanical properties.Using the defined testing method, a comparison was made on the basis ofpeak load, maximum displacement before failure, energy absorbed duringfracture, and stiffness. The energy of failure is the area under theload displacement curve measured from the origin to the point of firstfracture. Each of the above properties are based on a statisticalaverage of seven identical tests.

The tests showed that the fumed silica aggregates (Aerosil R972, 130,200, 380 and Cabosil EH5) resulted in a density of about 30% lowercompared to those where a different inorganic aggregate was added. Theother inorganic aggregates had a limited effect on the density of thecups, with the exception of Polymica which also decreased the density byabout 30% relative to cups using the other inorganic aggregates.

The dry peak load and stiffness of the cups containing fumed silica wereaffected to the same extent as the density; approximately 30% of eachwas lost compared to cups produced without fumed silica. The drydisplacement-to-failure and energy-to-failure measurements exhibitedlittle or no change due to the addition of inorganic materials.

The addition of Mica 4 k, glass bubbles, Wollastonite, Polymica 400, andsilica sand did not affect the energy-to-failuredisplacement-to-failure, peak load, and stiffness to any significantdegree. The one exception was Mica 4 k, which had a 30% increase in peakload. The value for thermal properties were found to be in a band widthof about 4-10% of the value for cups produced with no starch-basedbinder substitute. The values were independent of the type of inorganicaggregate used.

Based on the above tests, fumed silica aggregates appear to be lesspreferred since they adversely affect the mechanical properties of thearticles. In contrast, the other inorganic aggregates can be used toreplace at least 20% by weight of the starch-based binder withoutsignificantly affecting the mechanical properties of the articles. It isbelieved that fumed silicas produce a detrimental effect as a result oftheir low strength in comparison to the other inorganic aggregates.

Examples 14-27

Cups were made using different concentrations of calcium carbonate todetermine the effect of replacing the relatively expensive starch-basedbinder with less expensive calcium carbonate filler. The same proceduresand apparatus as discussed in Examples 1-13 were used to make and testthe cups of Examples 14-27. Each of the moldable mixtures included thefollowing basic mix design measured by weight:

    ______________________________________                                        49.75%       combination Stalok 400 potato starch                                          and inorganic aggregate                                          49.75%       water                                                            0.5%         magnesium stearate                                               ______________________________________                                    

Tests were run for two different types of calcium carbonate (Gama Sperseand RO40) at 20, 40, 50, and 60 weight percent inorganic aggregate basedon the total weight of the combination of the starch-based binder andthe inorganic aggregate. The same tests were also run on a mixture ofGama Sperse to which 2% by weight of polyacrylamide has been added.

Summarized below are the selected compositions and the properties of theresulting 12 oz. cups.

    __________________________________________________________________________         Inorganic           Displace-                                                 Aggregate Thermal                                                                            Energy                                                                             ment to                                                                            Peak                                                 (weight                                                                            Density                                                                            Conduct.                                                                           to Fail                                                                            Failure                                                                            load                                                                              Stiffness                                   Example                                                                            %)   (g/cc)                                                                             (W/m · K)                                                                 (mJ) (%)  (N) (N/m)                                       __________________________________________________________________________    Gama Sperse                                                                   14   0    0.19 0.044                                                                              7.0  2.9  3.2 6.0                                         15   20   0.21 0.046                                                                              6.0  2.9  2.5 5.0                                         16   40   0.24 0.052                                                                              6.0  2.5  --  --                                          17   50   0.27 0.054                                                                              6.0  2.2  4.5 6.5                                         18   60   0.28 0.053                                                                              6.0  2.1  4.6 6.0                                         Gama Sperse w/ 2% polyacrylamide                                              19   0    0.16 --   4.5  2.5  2.4 4.0                                         20   20   0.19 0.043                                                                              8.0  3.4  2.7 6.0                                         21   40   0.21 0.045                                                                              7.0  2.6  3.2 5.5                                         22   50   0.24 0.050                                                                              7.5  2.9  3.0 5.4                                         RO40                                                                          23   0    0.19 0.044                                                                              7.0  2.9  3.2 6.0                                         24   20   0.21 0.044                                                                              6.5  2.9  2.5 5.5                                         25   40   0.25 0.044                                                                              4.0  2.5  2.8 4.5                                         26   50   0.30 0.050                                                                              4.0  2.2  3.5 --                                          27   60   0.38 0.058                                                                              4.5  2.1  4.5 6.0                                         __________________________________________________________________________

The tests showed that the density of the articles increasesapproximately 0.8% for each weight percent of added Gama Sperse or R040calcium carbonates. This relationship held true for the full range ofGama Sperse (0-60% by weight) and for R040 in a range from 0-40% byweight. Adding higher than 40% R040 by weight roughly doubled the rateof increase of the density. The effect was similar for the samples thatcontained Gama Sperse with 2% polyacrylamide by weight.

The thermal conductivity results were somewhat unclear; however, therewas an increase in conductivity as the fraction of the inorganicaggregate was increased. The increase was in the order of about 0.2% perweight percent of calcium carbonate added.

The addition of calcium carbonate had little effect on theenergy-to-failure, displacement-to-failure, or the peak load. Althoughthe dry stiffness was substantially constant initially, it exhibited anincrease of about 50% at the highest weight fractions of 50 and 60%.Based on the above tests, there was only a limited detrimental effect onthe mechanical behavior by substituting up to 60% of starch-based binderwith calcium carbonate.

Examples 28-39

Cups were made using different types of calcium carbonate to determinetheir effect on the final article. The same procedures and apparatus setforth in Examples 1-13 were used to make and test the cups of thepresent examples. Each of the moldable mixtures included the followingcomponents by weight:

    ______________________________________                                        39.8%        Stalok 400 (modified potato starch)                              9.95%        calcium carbonate                                                49.5%        water                                                            0.5%         magnesium stearate.                                              ______________________________________                                    

Summarized below is a list of the selected types of calcium carbonateand the properties resulting from their use.

    __________________________________________________________________________                            Displace-                                                  Calcium   Thermal                                                                            Energy                                                                            ment to                                                    Carbonate                                                                           Density                                                                           Conduct.                                                                           to Fail                                                                           Failure                                                                            Peak load                                                                          Stiffness                                   Example                                                                            Aggregate                                                                           (g/cc)                                                                            (W/m · K)                                                                 (mJ)                                                                              (%)  (N)  (N/m)                                       __________________________________________________________________________    28   None  0.19                                                                              0.044                                                                              7   2.9  6.0  3.1                                         29   Gama  0.22                                                                              0.047                                                                              6   2.9  5.0  2.5                                              Sperse                                                                   30   Carbital 50                                                                         0.19                                                                              0.045                                                                              9   3.5  7.0  2.7                                         31   RO40  0.22                                                                              0.46 7   4.1  5.5  2.7                                         32   Albacar                                                                             0.19                                                                              0.046                                                                              6   4.1  4.0  1.5                                         33   Albacar Lo                                                                          0.19                                                                              0.047                                                                              --  --   --   --                                          34   Multiflex                                                                           0.25                                                                              0.048                                                                              6   2.6  5.5  3.1                                              MM w/211                                                                 35   RX    0.24                                                                              0.043                                                                              7   2.5  6.0  3.5                                              3694w/211                                                                36   Heavy 0.24                                                                              0.049                                                                              6   2.5  5.5  3.5                                              w/211                                                                    37   RX 3697                                                                             0.25                                                                              0.048                                                                              6   2.5  6.0  3.8                                              w/211                                                                    38   Albacar Lo                                                                          0.24                                                                              0.045                                                                              7   2.5  6.0  3.7                                              w/211                                                                    39   Ultra Phlex                                                                         0.17                                                                              0.045                                                                              8   3.7  5.0  2.0                                              w/211                                                                    __________________________________________________________________________

The tests revealed that for a 20 weight percent by solids addition of acalcium carbonate aggregate, the mechanical and thermal properties ofthe resulting cups were only moderately affected by the type of calciumcarbonate used. The changes in cup densities were minimal, being nogreater than about 10%. The thermal conductivities deviated from that ofthe reference cups by only about 5%, independent of the type of calciumcarbonate used.

The energies-to-failure showed a slightly higher value (about 20%) forCarbital 50 then those of the articles made using other calciumcarbonate aggregates, which were all approximately at the same level asthe reference cups. The displacement-to-failure and peak load wererelatively insensitive to the different kinds of calcium carbonateaggregates used except for Albacar. Albacar resulted in the lowestvalues in these categories. The cups that contained 20% calciumcarbonate possessed about the same stiffness as the cups made without aninorganic aggregate, the exception being Albacar and Ultra Phlex, whichresulted in cups having about half the stiffness.

In general, the different types of calcium carbonate aggregates hadsimilar effects on the properties of the final cups. The most notableexception was Albacar, which had a detrimental effect on severalproperties.

Examples 40-44

Cups were made using collamyl starch with different concentrations ofcalcium carbonate to determine the effect of using collamyl starch. Thesame procedures and apparatus set forth in Examples 1-13 were used tomake and test the cups of Examples 40-44. A base mixture was firstprepared by combining the following components by weight:

    ______________________________________                                        49.75%           collamyl starch and                                                           RO40 calcium carbonate                                       49.75%           water                                                        0.5%             magnesium stearate.                                          ______________________________________                                    

The calcium carbonate was added to the mixture in amounts of 20, 40, 50,and 60% by total weight of the calcium carbonate and starch-basedbinder. Summarized below are the properties of the articles made usingdifferent percentages of calcium carbonate.

    __________________________________________________________________________         Calcium            Displace-                                                  Carbonate Thermal                                                                            Energy                                                                            ment to                                                    Aggregate                                                                           Density                                                                           Conduct.                                                                           to Fail                                                                           Failure                                                                            Peak load                                                                          Stiffness                                   Example                                                                            (weight %)                                                                          (g/cc)                                                                            (W/m · K)                                                                 (mJ)                                                                              (%)  (N)  (N/m)                                       __________________________________________________________________________    40   0     0.17                                                                              0.043                                                                              6   3.5  4.5  1.9                                         41   20    0.17                                                                              0.043                                                                              7   4.3  4.5  1.7                                         42   40    0.24                                                                              0.046                                                                              7   3.5  5.2  2.2                                         43   50    0.27                                                                              0.045                                                                              7   3.2  5.8  2.5                                         44   60    0.32                                                                              0.053                                                                              7   2.6  6.5  3.5                                         __________________________________________________________________________

The increase in density was negligible for the first 20% of RO40 calciumcarbonate that was added. For higher concentrations, the increase wassubstantial, being about 2% for each weight percent of added R040.Increases in the thermal conductivity followed a similar pattern as forthe density. The increase in thermal conductivity for concentrations ofR040 exceeding 20% was about 0.5% per percent of added RO40. The energyand displacement-to-failure for the cups was largely unaffected by theaddition of RO40. The peak load increased linearly at the rate of about1% per percent of added RO40. The stiffness curve was similar to thedensity curve; a relatively flat region up to 20% RO40 and a linearincrease for higher concentrations. The rate of increase in stiffnesswas approximately 1% for each percent of added RO40 in mixturesexceeding 20% RO40.

Based on the above observations, collamyl starch can be used to make thearticles of the present invention. Furthermore, relatively highconcentrations of calcium carbonate can be added to mixtures containingcollamyl starch without significantly reducing the desired mechanicalproperties.

Examples 45-52

Cups were made using different types of admixtures to determine theireffects, if any, on the properties of the mixtures. The same proceduresand apparatus set forth in Examples 1-13 were used to make and test thecups of the present examples. A base mixture was first prepared bycombining the following components by weight:

    ______________________________________                                        39.8%        Stalok 400 (modified potato starch)                              9.95%        RO40 calcium carbonate                                           49.5%        water                                                            0.5%         magnesium stearate.                                              ______________________________________                                    

Admixtures, including Methocel® 240, Tylose® 15002 and polyvinyl alcohol(PVA), were then combined to the mixture by weight percentage of thetotal solids in the mixture. Summarized below is a list of the moldablemixtures and the properties resulting from their use.

    __________________________________________________________________________                             Displace-                                                            Thermal                                                                            Energy                                                                            ment to                                                                            Peak                                                 Admixtures                                                                          Density                                                                            Conduct.                                                                           to Fail                                                                           Failure                                                                            load                                                                              Stiffness                                   Example                                                                            (weight %)                                                                          (g/cc)                                                                             (W/m · K)                                                                 (mJ)                                                                              (%)  (N) (N/m)                                       __________________________________________________________________________    45   None  0.26 0.045                                                                              4   2.2  4.5 2.8                                         PVA                                                                           46   1.9   0.26 0.046                                                                              6   3.1  5.5 2.7                                         47   2.9   0.27 0.048                                                                              5   2.6  5.5 3.3                                         48   3.4   0.26 0.044                                                                              4   2.8  5.0 2.8                                         Methocel ® 240                                                            49   0.5   0.19 0.045                                                                              6   3.4  5.5 2.3                                         50   1.0   0.18 0.052                                                                              8   6.0  4.5 0.9                                         Tylose ® 15002                                                            51   0.5   0.23 0.044                                                                              7   4.1  5.0 1.8                                         52   1.0   0.19 0.049                                                                              3   3.1  3.5 1.7                                         __________________________________________________________________________

The addition of PVA was shown to have little effect on the densities,thermal conductivities, or mechanical properties of the cups madetherefrom. Methocel®240 and Tylose® 15002 affected the density slightly.The density decreased just over 20% per each addition of 1% of eitheradmixture. The thermal conductivity increased about 10% for the sameadditions. Methocel® 240 had a positive effect on the energy anddisplacement-to-failure measurements for dry cups. The energy-to-failurevalues doubled for each 1% addition, whereas the displacement-to-failurevalues showed an improvement of 2.5 times. The peak load dropped about20% for each 1% addition of Methocel® 240, while the stiffness fell morethan 70%. A 0.5% addition of Tylose® 15002 increased theenergy-to-failure by 60%, the displacement-to-failure by 80% and thepeak load by 10%. These increases disappeared with a further (0.5%)addition of Tylose® 15002. The stiffness of dry cups was halved byadditions of 1% of either Methocel® or Tylose®.

Generally, PVA was found to have a minimal impact on the properties ofthe formed cups. Methocel® 240 and Tylose® 15002 were found to eithermaintain or improve the properties of the cups at lower concentrations.The benefits, however, were lost as the concentration of each wasincreased.

Examples 53-57

To study the synergistic effect of some admixtures, moldable mixtureswere prepared containing varying amounts of RO40 calcium carbonate, bothwith and without the additives Dispex® A40 and Methocel® 240. The sameprocedures and apparatus set forth in Examples 1-13 were used to makeand test the cups of Examples 53-57. The cups were made from fivedifferent mixtures. Mixture 1 contained the following components byweight: 49.75% water, 0.5% magnesium stearate, 19.9% RO40 calciumcarbonate, and 29.85% Stalok 400 (modified potato starch). Mix 1 furthercontained 2% Dispex and 0.5% Methocel® 240 by weight of the combinedstarch-based binder and calcium carbonate. Mixture 2 was similar toMixture 1, except that the percentage of calcium carbonate was increasedto 29.85%, while the starch-based binder was decreased to 19.9%. InMixture 3, the calcium carbonate was further increased to 39.8%, thestarch-based binder decreased to 9.95%, and the other components keptthe same as in Mixture 1. Mixture 4 was similar to Mixture 1, exceptthat Dispex was not added. Finally, Mixture 5 was similar to Mix 3,except that Methotel® 240 was not added.

Summarized below are the properties of the cups made from the fivemixtures:

    __________________________________________________________________________                             Displace-                                                           Thermal                                                                            Energy                                                                             ment to                                                                            Peak                                                      Density                                                                            Conduct.                                                                           to Fail                                                                            Failure                                                                            load                                                                              Stiffness                                   Example                                                                            Mixture                                                                            (g/cc)                                                                             (W/m · K)                                                                 (mJ) (%)  (N) (N/m)                                       __________________________________________________________________________    53   Mixture 1                                                                          0.23 0.049                                                                              5    2.9  4.0 1.7                                         54   Mixture 2                                                                          0.25 0.049                                                                              3    2.9  3.0 1.3                                         55   Mixture 3                                                                          0.32 0.057                                                                              --   --   --  --                                          56   Mixture 4                                                                          0.26 0.044                                                                              7    3.5  5.5 2.3                                         57   Mixture 5                                                                          0.32 0.052                                                                              4    2.1  3.0 2.1                                         __________________________________________________________________________

The tests demonstrate that the densities of the articles increased asthe concentration of calcium carbonate was increased. The densities ofthe articles increased, however, if either Dispex A40 or Methocel® 240was not included in the mix design. The thermal conductivity exhibited asimilar increase with increasing calcium carbonate concentration. Theenergy-to-failure and displacement-to-failure decreased as higher levelsof R040 were included. The samples without Dispex A40 displayed about30% higher values, whereas the samples produced from a mixture withoutMethocel® 240 had slightly lower levels of performance. The peak loadand stiffness both exhibited inferior levels when Dispex A40 andMethocel® were added to the mixtures.

Although the admixtures were useful in producing articles having higherconcentrations of inorganic aggregates, both Dispex A40 and Methocel®240 produced articles having lower densities and inferior mechanicalproperties.

Examples 58-62

Cups were made using different mounts of the cross-linking admixtureSunrez 747 to determine its effect on the moldable mixture. The sameprocedures and apparatus set forth in Examples 1-13 were used to makeand test the cups of Examples 58-62. A base mixture was first preparedby combining the following components by weight:

    ______________________________________                                        28.15%       Stalok 400 (modified potato starch)                              19.9%        RO40 calcium carbonate                                           1.7%         PVA                                                              49.75%       water                                                            0.5%         magnesium stearate.                                              ______________________________________                                    

The base mixture was then varied by incrementally increasing theconcentration of Sunrez 747 by weight of total solids in the mixtureover a range from 2% to 20%. Summarized below are the percentages ofSunrez 747 and the corresponding properties of the resulting cups.

    __________________________________________________________________________         Sunrez              Displace-                                                 747       Thermal                                                                            Energy                                                                             ment to                                                                            Peak                                                 (weight                                                                            Density                                                                            Conduct.                                                                           to Fail                                                                            Failure                                                                            load                                                                              Stiffness                                   Example                                                                            %)   (g/cc)                                                                             (W/m · K)                                                                 (mJ) (%)  (N) (N/m)                                       __________________________________________________________________________    58   0    0.26 0.044                                                                              4    2.8  4.8 2.5                                         59   2    0.25 0.048                                                                              5    2.8  5.0 2.6                                         60   5    0.24 0.048                                                                              4    2.8  4.8 2.5                                         61   10   0.23 0.048                                                                              7    4.4  4.2 1.5                                         62   20   0.24 0.046                                                                              4    3.4  4.0 1.8                                         __________________________________________________________________________

The tests showed that Sunrez 747 had limited effect on the cup density.Initially, the density decreased about 2% for each percent of addedSunrez 747. This relationship persisted up to about 5% of the admixture,after which the cup density leveled off. The thermal conductivity showedan initial increase of approximately 4% for the first 2% of added Sunrez747, but then leveled out. The mechanical properties of the cups alsopeaked early with the addition of Sunrez 747. The energy anddisplacement-to-failure of cups showed only minor increases up to 10%and then fell off slightly again. The peak load was fairly level with anapex at 2%. The stiffness curve approximated a step function. There wasa plateau where there was no effect of Sunrez 747 addition up to 5%.There was a dramatic decrease in stiffness, roughly 50%, between 5 and10%; thereafter the stiffness was not affected. In general, moderateimprovements in the various properties were found where lowerconcentrations of Sunrez 747 were added.

Examples 63-70

Five mix designs were evaluated using varying concentrations of calciumcarbonate (RO40), and different types of starch, in order to determinethe minimum processing time and filling weight at four processingtemperatures (160° C., 180° C., 200° C., and 220° C.). As used in theexamples, specification, and appended claims, the term "processing time"refers to the time necessary to heat the mixture into a form-stablearticle. The composition of the five mixtures were as follows:

    ______________________________________                                               Stalok 400                                                                              Hylon VII RO40  Mg Stearate                                                                           Water                                       (g)       (g)       (g)   (g)     (g)                                  ______________________________________                                        Mixture 1                                                                            500       0         0     5       500                                  Mixture 2                                                                            350       50        100   5       450                                  Mixture 3                                                                            300       50        150   5       440                                  Mixture 4                                                                            250       50        200   5       425                                  Mixture 5                                                                            200       50        250   5       410                                  ______________________________________                                    

Hylon VII is a type of modified corn starch that was substituted forpart of the Stalok 400. The moldable mixtures were prepared using theprocedures set forth in Example 1-13. Once the mixtures were prepared, aHAAS LB-STA machine was used to make 16 oz. cups having thicknesses ofabout 4 mm and waffled exteriors. The resulting filling weights andprocessing times at the selected temperatures are summarized as follows:

    ______________________________________                                                  Processing Time (sec)                                               Ex-   Temp.   Mixture Mixture                                                                              Mixture                                                                              Mixture                                                                              Mixture                            ample (°C.)                                                                          1       2      3      4      5                                  ______________________________________                                        63    220     40      40     40     40     40                                 64    200     50      50     50     45     45                                 65    180     75      75     75     75     75                                 66    160     170     170    170    165    160                                ______________________________________                                    

    ______________________________________                                                  Filling Weight (g)                                                  Exam- Temp.   Mixture Mixture                                                                              Mixture                                                                              Mixture                                                                              Mixture                            ple   (°C.)                                                                          1       2      3      4      5                                  ______________________________________                                        67    220     30.5    32.2   34.4   37.9   41.6                               68    200     33      31.5   35.6   39.3   43.9                               69    180     31.4    33.5   35.5   37.6   44.1                               70    160     31.7    33.7   34.1   39.7   43.9                               ______________________________________                                    

As expected, the tests revealed that the processing times decreased asthe processing temperatures increased. Although the decrease inprocessing time was greatest for increases in processing temperatures atthe lower ranges, the decrease in processing time was most dramaticwhere calcium carbonate was included at the higher concentration ranges.The tests also revealed that the minimum filling weight increased withhigher concentrations of calcium carbonate. However, the filling weightwas independent of the mold temperature.

Examples 71-78

The same compositions and processing parameters defined in Examples63-70 were used to determine the minimum processing times and fillingweights at four processing temperatures (160° C., 180° C., 200° C., and220° C.) to produce 12 oz. cups having a smooth surface. Theexperimental results of the effects on the processing time and minimumfilling weight are summarized below.

    ______________________________________                                                  Processing Time (sec)                                               Ex-   Temp.   Mixture Mixture                                                                              Mixture                                                                              Mixture                                                                              Mixture                            ample (°C.)                                                                          1       2      3      4      5                                  ______________________________________                                        71    220     35      35     35     35     35                                 72    200     40      40     40     40     40                                 73    180     80      80     80     75     75                                 74    160     110     110    110    110    110                                ______________________________________                                    

    ______________________________________                                                  Filling Weight (g)                                                  Ex-   Temp.   Mixture Mixture                                                                              Mixture                                                                              Mixture                                                                              Mixture                            ample (°C.)                                                                          1       2      3      4      5                                  ______________________________________                                        75    220     28.7    29.3   33.2   37.5   41                                 76    200     28      31.6   33.4   37.5   40.7                               77    180     30.5    31.5   33.8   38.8   42                                 78    160     28.2    31.5   36.5   38.2   40                                 ______________________________________                                    

The test revealed findings similar to those outlined above in Examples63-70.

Examples 79-86

The same compositions and processing parameters defined in Examples63-70 were used to determine the minimum processing times and fillingweights at four processing temperatures (160° C., 180° C., 200° C., and220° C.) to produce "clam-shell" containers having a smooth surface. Theexperimental results regarding the processing time and minimum fillingweight are summarized below.

    ______________________________________                                                  Processing Time (sec)                                               Ex-   Temp.   Mixture Mixture                                                                              Mixture                                                                              Mixture                                                                              Mixture                            ample (°C.)                                                                          1       2      3      4      5                                  ______________________________________                                        79    220     30      30     30     30     30                                 80    200     35      35     35     35     35                                 81    180     45      45     45     45     45                                 82    160     50      50     50     50     50                                 ______________________________________                                    

    ______________________________________                                                  Filling Weight (g)                                                  Ex-   Temp.   Mixture Mixture                                                                              Mixture                                                                              Mixture                                                                              Mixture                            ample (°C.)                                                                          1       2      3      4      5                                  ______________________________________                                        83    220     19.7    24.1   25.6   29.8   31.2                               84    200     19.0    23.4   24.7   27.8   32.5                               85    180     17.9    23.4   24.6   28.7   30.5                               86    160     17.1    23.4   25.0   28.0   30.5                               ______________________________________                                    

The tests revealed finding similar to those outlined in Examples 63-70.

Examples 87-91

Using the same process as in Examples 1-13, 12 oz. cups were made usingdies at a temperature of 200° C. The mixture for manufacturing the cupconsisted of the following components by weight:

    ______________________________________                                        24.95%       Stalok 400 (modified potato starch)                              19.9%        RO40 calcium carbonate                                           4.9%         Hylon VII (modified corn starch)                                 49.75%       water                                                            0.5%         magnesium stearate.                                              ______________________________________                                    

The dried cups were placed in a high humidity chamber having a relativehumidity of about 95% and a temperature of about 45° C. The cups wereremoved after varying levels of moisture had been absorbed by thestarch-bound structural matrix of the cups and tested to determine theirmechanical properties. The respective moisture contents andcorresponding mechanical properties are outlined below:

    ______________________________________                                        BASE MIXTURE-10% Hylon-40% CaCO3                                                     Moisture  Peak Load  Displacement to                                                                         Energy                                  Examples                                                                             Content   (N)        Failure (%)                                                                             (mJ)                                    ______________________________________                                        87     0         5.5        2.9       5                                       88     2         8.5        3.7       12                                      89     5.5       10.5       11.8      45                                      90     7.5       9.0        23.5      65                                      91     9.5       --         24.3      40                                      ______________________________________                                    

The test results reveal a roughly linear correlation between themoisture content and the mechanical properties for low moisturecontents. As the moisture content increased, the mechanical propertiesimprove.

Examples 92-94

Using the same processing parameters set forth in Examples 1-13, 12 oz.cups were made from moldable mixtures having varying percentages ofcalcium carbonate and relatively constant viscosities to determine theeffect of calcium carbonate on the required water content and time forremoving the water. Summarized below are the compositions tested and therequired times to produce a form-stable article having a finishedsurface.

    ______________________________________                                               Calcium  Starch-based                                                                             Magnesium     Process                                     Carbonate                                                                              binder     Stearate                                                                              water Time                                 Example                                                                              (g)      (g)        (g)     (g)   (sec)                                ______________________________________                                        92     250      250        10      425   50-55                                93     350      150        10      350   35-40                                94     400      100        10      285   30                                   ______________________________________                                    

The results show that with increased concentrations of calciumcarbonate, less water is needed to obtain a mixture having a constantviscosity. Furthermore, as a result of having less water, the requiredprocessing time to produce a form-stable article was decreased.

Examples 95-114

The same five compositions and baking times set forth in Examples 63-70were used to make 16 oz. cups having a waffled surface. The dried cupswere subsequently placed on a scale within a humidity chamber at 45° C.and a relative humidity of 90%. The rate of moisture absorption of thecups was then determined by plotting the weight of the cups as afunction of time. Summarized below are tables showing the percentmoisture absorption at selected time intervals for each of the fivemixtures. A separate table is provided for the cups made at temperaturesof 160° C., 180° C., 200° C., and 220° C.

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 160° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        95    Mixture 1 5.0      8.0    11.0    --                                    96    Mixture 2 5.0      7.5    10.0    12                                    97    Mixture 3 3.5      6.0    8.0     10                                    98    Mixture 4 3.5      5.5    7.5      9                                    99    Mixture 5 3.0      5.0    6.0      7                                    ______________________________________                                    

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 180° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        100   Mixture 1 6.5      11     12      --                                    101   Mixture 2 6.0      9.0    11.5    13.5                                  102   Mixture 3 4        6.5    9.0     11.0                                  103   Mixture 4 4        6.0    8.0      9.5                                  104   Mixture 5 2.5      4.5    6.0      7.0                                  ______________________________________                                    

    ______________________________________                                        Ex-             Moisture Absorption weight (%) at 200° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        105    Mixture 1                                                                              5.5      10.0   --      --                                    106    Mixture 2                                                                              4.5      7.0    9.0     11.5                                  107    Mixture 3                                                                              4.5      7.0    9.0     11.0                                  108    Mixture 4                                                                              4.5      7.0    8.5     10.0                                  109    Mixture 5                                                                              4.5      6.5    8.0      9.0                                  ______________________________________                                    

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 220° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        110    Mixture 1                                                                              5.0      9.5    13.0    --                                    111    Mixture 2                                                                              4.5      8.5    11.5    --                                    112    Mixture 3                                                                              4.0      7.0    9.0     11.0                                  113    Mixture 4                                                                              4.0      7.0    9.0     11.0                                  114    Mixture 5                                                                              3.0      5.0    6.5      8.0                                  ______________________________________                                    

The tests showed that the rate of moisture absorption decreases for allcompositions. That is, the more moisture contained within an article,the slower the article absorbs additional moisture. The tests alsoshowed that cups having increased concentrations of calcium carbonateabsorb moisture at a lower rate. There is, however, no systematicvariation on the absorption rates as a function of the differentprocessing temperatures. It is believed that the differences betweentables are due to statistical variations.

Examples 115-136

The same five mixtures and processing times set forth in Examples 63-70were used to make 12 oz. cups having a smooth surface. The dried cupswere subsequently placed on a scale within a humidity chamber at 45° C.and a relative humidity of 90%. The rate of moisture absorption of thecups was then determined by plotting the weight of the cups versus time.Summarized below are tables showing the percent moisture absorption atselected time intervals for each of the five mixture. A separate tableis provided for the cups made at mold temperatures of 160° C., 180° C.,200° C., and 220° C.

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 160° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        115    Mixture 1                                                                              3.5      6.0    9.0     --                                    116    Mixture 2                                                                              3.5      6.5    9.0     11.0                                  117    Mixture 3                                                                              3.5      6.0    8.0     10.0                                  118    Mixture 4                                                                              3.5      6.0    8.0      8.5                                  119    Mixture 5                                                                              3.5      5.5    7.0      8.0                                  ______________________________________                                    

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 180° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        120    Mixture 1                                                                              4.5      8.0    11.5    --                                    121    Mixture 2                                                                              3.0      6.0    8.5     10.0                                  122    Mixture 3                                                                              3.0      6.0    8.0      9.5                                  123    Mixture 4                                                                              2.5      5.0    6.5      8.0                                  124    Mixture 5                                                                              1.5      5.0    8.0      9.5                                  ______________________________________                                    

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 200° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        125    Mixture 1                                                                              4.5      8.5    12.0    --                                    126    Mixture 2                                                                              4.0      7.0    10.0    11.0                                  127    Mixture 3                                                                              3.0      5.5    8.0     10.0                                  128    Mixture 4                                                                              3.0      5.5    7.5      9.0                                  129    Mixture 5                                                                              3.0      5.0    7.0      8.0                                  ______________________________________                                    

    ______________________________________                                        Ex-             Moisture Absorption (weight %) at 220° C.              ample Composition                                                                             400 (sec)                                                                              800 (sec)                                                                            1200 (sec)                                                                            1600 (sec)                            ______________________________________                                        130    Mixture 1                                                                              4.5      3.5    11.5    --                                    131    Mixture 2                                                                              4.0      2.0    10.0    12.0                                  132    Mixture 3                                                                              2.5      5.5    8.0     10.0                                  133    Mixture 4                                                                              2.5      5.5    7.5      8.5                                  134    Mixture 5                                                                              2.0      4.0    6.0      6.5                                  ______________________________________                                    

The tests showed that the rate of moisture absorption decreases for allcompositions. That is, the more moisture contained within an article,the slower the articles absorb additional moisture. The tests alsoshowed that cups having increased concentrations of calcium carbonateabsorb moisture at a lower rate. There is, however, no systematicvariation of the absorption rates as a function of the differentprocessing temperatures. It is believed that the differences betweentables are due to statistical variations.

Examples 135-139

Using the five mixtures set forth in Examples 63-70, 12 oz. cups havinga smooth surface were produced using a mold temperature of 200° C. Thecups were subsequently placed in a high humidity chamber at 45° C. and90% humidity. Selected cups were periodically removed during theconditioning stage and tested in order to determine the moisture contentnecessary to yield an article having a 10 mmdisplacement-before-failure. A displacement of 10 mm was arbitrarilychosen as providing a cup with a sufficient amount of damage toleranceto make the cup useful. The resulting moisture contents necessary toimpart the desired property to the cups at the different mixtures aresummarized below:

    ______________________________________                                                             Moisture   Displacement to                               Examples Mixture     Content (%)                                                                              Failure (%)                                   ______________________________________                                        135      Mixture 1   8.0        14.7                                          136      Mixture 2   6.7        14.7                                          137      Mixture 3   6.1        14.7                                          138      Mixture 4   5.5        14.7                                          139      Mixture 5   4.9        14.7                                          ______________________________________                                    

The tests revealed that as the percentage of calcium carbonate wasincreased in the mixtures, the required amount of moisture needed toimpart the desired displacement-to-failure decreased. Comparing thepresent test results with those in Examples 95-114, shows that, althoughmixtures having more calcium carbonate absorb moisture at a slower rate,such mixtures require less moisture to obtain the desired properties.

Examples 140-146

Articles were made using different types of calcium carbonate todetermine the effect of the particle size and packing density of theinorganic aggregate. Mixtures were made from three different types ofcalcium carbonate: Carbital 75, RO40, and Marblend. The basic chemicalcomposition for each type of calcium carbonate was the same; however,the particle size distribution, average particle size, and naturalpacking density (or non compressed packing density), as shown below,varied greatly.

    ______________________________________                                        Type of Calcium                                                                            Average Particle Size                                                                       Natural Packing                                    Carbonate    (μm)       Density                                            ______________________________________                                        Carbital 75  2.395         0.3593                                             RO40         40.545        0.6869                                             Marblend     68.468        0.7368                                             ______________________________________                                    

    ______________________________________                                        Gradation of Carbital 75                                                      Sieve Opening   Retained Passing                                              (μm)         %        %                                                    ______________________________________                                        18.000          0.00     100.00                                               5.470           10.00    90.00                                                3.043           25.00    75.00                                                1.583           50.00    50.00                                                0.862           75.00    25.00                                                0.490           90.00    10.00                                                ______________________________________                                    

    ______________________________________                                        Gradation of RO40                                                             Sieve Opening   Retained Passing                                              (μm)         %        %                                                    ______________________________________                                        275.000         0.00     100.00                                               134.700         10.00    90.00                                                82.150          25.00    75.00                                                41.308          50.00    50.00                                                14.190          75.00    25.00                                                2.782           90.00    10.00                                                ______________________________________                                    

    ______________________________________                                        Gradation of Marblend                                                         Sieve Opening   Retained Passing                                              (μm)         %        %                                                    ______________________________________                                        1000.00         0.00     100.00                                               338.100         10.00    90.00                                                212.200         25.00    75.00                                                36.190          50.00    50.00                                                12.160          75.00    25.00                                                3.761           90.00    10.00                                                ______________________________________                                    

These tables show that, of the three types of calcium carbonate tested,Carbital 75 had by far the smallest average particle size and thesmallest particle size distribution, Marblend had the largest, and KO40was intermediate. Each mixture contained one type of calcium carbonate,Stalok 400 potato starch and water, while no mold releasing agent wasused. The mixtures were prepared according to the procedures set forthin Examples 1-13 and then placed between molds having a temperature ofabout 200° C. The articles were removed from the molds once they hadobtained form-stability. The molds were nickel-Teflon coated and hadcomplementary shapes defined to produce a platter. The formed platterswere approximately 25 cm long, 18 cm wide, and 3 mm thick. Outlinedbelow are the components for each mixture, the weight of the finalplatter, and the processing time.

    ______________________________________                                               Calcium                   Platter                                                                             Processing                                    Carbonate Stalok 400                                                                              Water weight                                                                              Time                                   Example                                                                              (g)       (g)       (g)   (g)   (sec)                                  ______________________________________                                        Calcium Carbonate Carbital 75                                                 140    100       900       800   31.6  40                                     141    200       800       800   32.5  40                                     142    300       700       800   NA    NA                                     Calcium Carbonate RO40                                                        143    700       300       800   30.2  40                                     144    800       200       800   NA    NA                                     Calcium Carbonate Marblend                                                    145    700       300       800   30.2  40                                     146    800       200       800   NA    NA                                     ______________________________________                                    

Examples 140 and 141 produced form-stable articles having negligiblecracks or defects, although the plates of Example 140 were of somewhathigher quality than those of Example 141. In example 142, where theCarbital 75 was increased to 30% by weight of the total solids,crack-free, form-stable articles could not be made, regardless of theprocessing time. Examples 143 and 145 produced form-stable articleshaving negligible cracks or defects using 70% by weight of total solidsRO40 and Marblend. The best articles were formed in Example 145.Crack-free, form-stable articles could not be made in Examples 144 and146 where the concentration of RO40 and Marblend was increased to 80% byweight of the solids.

The above examples teach that functional articles can be made withhigher concentrations of inorganic aggregate by using an aggregatematerial which (1) has a larger average diameter (which yields anaggregate material having a lower specific surface area), and (2) whichhas a greater particle size distribution (which yields an aggregatematerial having a higher particle packing density). The maximum amountof Carbital 75 that could be used to produce functional articles was 20%by weight of the solids. In comparison, functional articles could bemade using 70% by weight of either RO40 or Marblend. The difference inthe concentration of aggregate that could be used is attributed to thefact that RO40 and Marblend had a natural packing density approximatelytwice that of Carbital 75. The difference is further attributed to thefact that RO40 and Marblend had an average particle size that wasapproximately twenty to thirty times larger than Carbital 75.

To illustrate, Carbital 75 had a relatively low packing density of about0.36. As the concentration of Carbital 75 increased and theconcentration of starch-based binder decreased, respectively, the volumeof interstitial space between the particles increased. As a result, moreof the starch-based binder and water was being used to fill theinterstitial space as opposed to coating the particles. Furthermore,since the Carbital 75 had a relatively small average particle size (and,hence, a larger specific surface area), more water and starch-basedbinder were needed to coat the aggregate particles. Eventually, when theconcentration of Carbital 75 reached 30% by weight of the solids, thevolume of interstitial space was so large that there was insufficientwater to adequately disperse the starch-based binder and insufficientstarch-based binder to adequately bind the aggregate particles into aform-stable, crack-free structural matrix.

In contrast, the Marblend had a much higher packing density of about0.73 and a larger average particle size. Accordingly, even at the higherconcentration of 70% Marblend by weight of solids, the interstitialspace was sufficiently small to permit the starch-based binder and waterto adequately bind the aggregate particles into a functional article. At80% Marblend by weight of solids, however, the volume of interstitialspace was again too large for the starch-based binder and water toadequately bind the aggregate particles into a form-stable, crack-freestructural matrix. However, it would be expected that by using anaggregate having a packing density higher then that of Marblend, anarticle could be made having an even higher concentration of inorganicaggregates.

It is also noteworthy that the viscosity of the mixtures decreased asthe concentration of Carbital 75 increased and that the viscosity of themixtures increased with increased concentrations of RO40 and Marblend.As previously discussed, the starch-based binder absorbs the solvent. Byreplacing a portion of the starch-based binder with an inorganicaggregate, the amount of solvent that would have been absorbed by thestarch-based binder is free to lubricate the aggregate particles.However, the inorganic aggregate replacing the starch-based binder alsoproduces interstitial space which must be filled by the solvent.Accordingly, if the amount of solvent freed by the removal of thestarch-based binder is smaller than the volume of interstitial spacecreated by the addition of the aggregate, then the viscosity of themixture increases. This process is illustrated by the use of Carbital75. In contrast, if the mount of solvent freed by the removal of thestarch-based binder is larger than the volume of interstitial spacecreated by the addition of more aggregate, then the viscosity of themixture decreases. This process is illustrated by the RO40 and Marblend.

Examples 147-151

In the following examples, each of the components was held constantexcept for the starch-based binder, which was gradually substituted withrice flour. Because rice flour includes a high percentage of starch,along with some protein, it would be expected to have a binding effectwithin the structural matrix. In addition, the inert fraction would beexpected to act as an inert organic filler. All concentrations areexpressed as a percentage by weight of the overall mixture.

    ______________________________________                                                                               Magnesium                              Example                                                                              Stalok 400                                                                              Rice Flour RO40 Water Stearate                               ______________________________________                                        147    24.8%       0%       24.8%                                                                              49.5% 0.5%                                   148    19.8%      5.0%      24.8%                                                                              49.5% 0.5%                                   149    14.9%      9.9%      24.8%                                                                              49.5% 0.5%                                   150    9.9%      14.9%      24.8%                                                                              49.5% 0.5%                                   151    5.0%      19.8%      24.8%                                                                              49.5% 0.5%                                   ______________________________________                                    

The compositions of these examples resulted in molded articles in whichthe average cell diameter of the cells decreased as the percentage ofthe rice flour was increased and the amount of Stalok 400 (potatostarch) was decreased. Hence, these examples show that the cell size canbe regulated through the use of controlled mixtures of starch-basedbinder of different origin. This, in turn, results in articles havingsignificantly different physical and mechanical properties. In thismanner, rice flour (or similar grain flours or alternative starchsources) can be used in varying amounts in order to carefully controlthe physical and mechanical properties of the resulting articlesmanufactured therefrom. The following are the average cell diameters andskin thicknesses of the articles manufactured using the mix designs ofExamples 147-151:

    ______________________________________                                        Example                                                                              Average Cell Diameter                                                                        Wall Thickness                                                                           Skin Thickness                               ______________________________________                                        147    670 μm      2.2 mm     300 μm                                    148    450 μm      2.4 mm     370 μm                                    149    370 μm      2.5 mm     330 μm                                    150    300 μm      2.3 mm     250 μm                                    151    300 μm      2.1 mm     200 μm                                    ______________________________________                                    

Example 152

In order to increase the average cell size and skin thickness, moldablemixtures are made which have decreased viscosity, even as low as 50 cpsat a shear rate of 100 rpm, by altering the base mixture of 49.75%Stalok 400 and inorganic aggregate (combined), 49.75% water, and 0.5%magnesium stearate. This base mixture has a viscosity of 300 cps at ashear rate of 100 rpm. The viscosity of the mixture can be reduced to 50cps at the same shear rate by adding more water or through the additionof 1% oil by weight.

Alternatively, in order to decrease the average cell size and skinthickness, the viscosity of the moldable mixture can be increased, evenup to 100,000 cps at the same shear rate, through the use of less waterand/or the addition of cellulosic thickeners (such as Methocel®).

Example 153

A mixture containing 24.8% Stalok 400, 24.8% inorganic aggregate, 49.5%water, and 0.5% magnesium stearate is formed by pregelating thestarch-based binder prior to the addition of the aggregate and moldrelease agent. The pregelation is carried out either through the use ofa precooking step or through the use of a pregelated starch-basedbinder. The precooking step is carded out by heating the vesselcontaining the starch-based binder mixture over a heated surface or bymicrowaving the mixture. The yield stress of these pregelated mixturesis between about 3 kPa to about 20 kPa. The mixtures produced by thismethod are fabricated into articles by the same processing techniquesused in the foregoing examples for a pourable mixture.

Examples 154-157

Moldable mixtures containing varying amounts of polyvinyl alcohol("PVA") were used to manufacture articles. It was found that the use ofPVA decreased the processing time.

    __________________________________________________________________________         Starch-based                                                                  binder Calcium                                                                             Mg        Polyvinyl                                                                           Process                                     Example                                                                            (StaLok)                                                                             Carbonate                                                                           Stearate                                                                           Water                                                                              Alcohol                                                                             Time                                        __________________________________________________________________________    154  500 g  500 g 20 g 883 g                                                                              1.7 g 45-50 sec                                   155  500 g  500 g 20 g 917 g                                                                              3.33 g                                                                              40-45 sec                                   156  500 g  500 g 20 g 950 g                                                                              5.0 g 40-45 sec                                   157  500 g  500 g 20 g 983 g                                                                              6.7 g 35-40 sec                                   __________________________________________________________________________

Examples 158-160

Mixtures were prepared that contained the following components andconcentrations in order to show the effect of solvent concentration onthe density and insulation ability of the articles manufacturedtherefrom.

    ______________________________________                                               Potato Starch                                                                            Calcium Carbonate                                                                         Magnesium                                                                             Water                                   Example                                                                              (g)        RO40 (g)    Stearate (g)                                                                          (g)                                     ______________________________________                                        158    500        500         10      100                                     159    500        500         10      200                                     160    500        500         10      300                                     ______________________________________                                    

The articles manufactured from the mixtures of Examples 158-160demonstrated that using less water resulted in a molded article havingsmaller cells, higher density, and lower insulation (higher thermalconductivity).

Example 161

A study was performed to determine the effect of varying the number ofvent holes within the molding apparatus used to manufacture cups on thestructure of the resulting molded cups. The moldable mixture of Example1 was formed into cups using different molding apparatus in which thenumber of vent holes was varied so that there were 2, 4, 6, 8, or 10vent holes of standard size, respectively. The density of the walls ofthe resulting cups increased as the number of vent holes increased,presumably because of the decrease in pressure that was able to buildup, which led to a lower expansion of the cells within the structuralmatrix of the cup walls. Hence, using fewer vent holes results in amolded article having wall that are less dense and which have largercells within the structural matrix.

Examples 162-169

Moldable mixtures are made which have a lightweight aggregate in orderto yield a more lightweight article having greater insulation abilityand lower density. The mixtures used to form such articles are set forthas follows:

    ______________________________________                                               Potato Starch                                                                            Perlite (% by                                                                              Magnesium                                                                             Water                                  Example                                                                              (g)        volume of mixture)                                                                         Stearate (g)                                                                          (g)                                    ______________________________________                                        162    500        5            10      500                                    163    500        10           10      500                                    164    500        15           10      500                                    165    500        25           10      500                                    166    500        40           10      500                                    167    500        55           10      500                                    168    500        65           10      500                                    169    500        85           10      500                                    ______________________________________                                    

The mixtures are formed into cups using the systems and methods setforth above. As the amount of perlite is increased, the resulting cuphas a lower density, thermal conductivity, increased stiffness, andincreased brittleness. The cups having the optimal balance of theforegoing properties are obtained by using a moldable mixture in thewhich the concentration of perlite ranges from between about 25% toabout 55% perlite by volume of the moldable mixture. However, using moreor less than these amounts may be desired for certain articles.

VII. SUMMARY

From the foregoing, it will be appreciated that the present inventionprovides improved inorganically filled compositions for manufacturingarticles that can be formed into a variety of objects presently formedfrom paper, cardboard, polystyrene, metal, glass, plastic, or otherorganic materials.

The present invention further provides inorganically filed articles thatcan be directly formed having the desired flexibility for their intendeduse.

The present invention additionally provides inorganically filledarticles that can simultaneously be formed with a coating.

The present invention also provides inorganically filled articles thatcan be formed having a smooth surface.

The present invention also provides compositions which yieldinorganically filled, cellular articles which have properties similar tothose of paper, paperboard, polystyrene, metal, glass, and plastic. Suchcompositions can be formed into a variety of containers and otherobjects using slightly modified, currently existing equipment.

The present invention further provides compositions for manufacturinginorganically filled, cellular articles which do not result in thegeneration of wastes involved in the manufacture of paper, paperboard,plastic, metal, glass, or polystyrene materials.

The present invention further provides compositions, which contain lesswater to be removed during the manufacturing process (as compared topaper manufacturing) in order to shorten the processing time and reducethe initial equipment capital investment. Further, the articles arereadily degradable into substances which are nontoxic and which arecommonly found in the earth.

In addition, the present invention provides compositions which makepossible the manufacture of containers and other articles at a costcomparable, and even superior, to existing methods of manufacturingpaper or polystyrene products.

The present invention also provides compositions which are less energyintensive, which conserve valuable natural resources, and which requirelower initial capital investments compared to those used in makingarticles from conventional materials.

Additionally, the present invention provides compositions formass-producing inorganically filled, cellular articles which can rapidlybe formed and substantially dried within a matter of minutes from thebeginning of the manufacturing process.

Finally, the compositions allow for the production of highlyinorganically filled, cellular materials having greater flexibility,flexural strength, toughness, moldability, and mass-producibilitycompared to materials having a high content of inorganic filler.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrated andnot restrictive. The scope of the invention is, therefore, indicated bythe appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. An article of manufacture comprising a starch-boundcellular matrix of starch and inorganic aggregate, the starch-boundcellular matrix comprising:a starch-based binder that has beensubstantially gelatinized by water and then hardened through the removalof a substantial quantity of the water by evaporation; and an inorganicaggregate dispersed throughout the starch-bound cellular matrix in aconcentration in a range from about 20% to about 90% by weight of totalsolids within the starch-bound cellular matrix,wherein the starch-boundcellular matrix has a thickness less than about 1 cm and degrades afterprolonged exposure to water.
 2. An article of manufacture as defined inclaim 1, wherein the starch-based binder includes a potato starch.
 3. Anarticle of manufacture as defined in claim 1, wherein the starch-basedbinder includes a wheat starch.
 4. An article of manufacture as definedin claim 1, wherein the starch-based binder is selected from the groupconsisting of starches derived from cereals, tubers, roots, and mixturesthereof.
 5. An article of manufacture as defined in claim 1, wherein thestarch-based binder is derived from a grain flour.
 6. An article ofmanufacture as defined in claim 1, wherein the starch-based binderincludes a plurality of different types of starches.
 7. An article ofmanufacture as defined in claim 1, wherein the starch-based binderincludes a modified starch.
 8. An article of manufacture as defined inclaim 1, wherein the starch-based binder is included in an amount in arange from about 10% to about 80% by weight of total solids within thestarch-bound cellular matrix.
 9. An article of manufacture as defined inclaim 1, wherein the starch-based binder is included in an amount in arange from about 30% to about 70% by weight of total solids within thestarch-bound cellular matrix.
 10. An article of manufacture as definedin claim 1, wherein the starch-based binder is included in an amount ina range from about 40% to about 60% by weight of total solids within thestarch-bound cellular matrix.
 11. An article of manufacture as definedin claim 1, wherein the inorganic aggregate includes calcium carbonate.12. An article of manufacture as defined in claim 1, wherein theinorganic aggregate includes sand.
 13. An article of manufacture asdefined in claim 1, wherein the inorganic aggregate includes a pluralityof different kinds of aggregates.
 14. An article of manufacture asdefined in claim 1, wherein the inorganic aggregate is selected from thegroup consisting of sandstone, glass beads, mica, clay, kaolin,limestone, silica, fused silica, alumina, and mixtures thereof.
 15. Anarticle of manufacture as defined in claim 1, wherein the inorganicaggregate is selected from the group consisting of perlite, vermiculite,hollow glass spheres, aerogel, exfoliated rock, and mixtures thereof.16. An article of manufacture as defined in claim 1, wherein theinorganic aggregate imparts a color to the mixture.
 17. An article ofmanufacture as defined in claim 1, wherein the inorganic aggregate has aspecific surface area in a range from about 0.1 m² /g to about 400 m²/g.
 18. An article of manufacture as defined in claim 1, wherein theinorganic aggregate has a specific surface area in a range from about0.15 m² /g to about 50 m² /g.
 19. An article of manufacture as definedin claim 1, wherein the inorganic aggregate has a specific surface areain a range from about 0.2 m² /g to about 2 m² /g.
 20. An article ofmanufacture as defined in claim 1, wherein the inorganic aggregateincludes a lightweight aggregate which lowers the thermal conductivityof the article.
 21. An article of manufacture as defined in claim 1,wherein the inorganic aggregate is included in an amount in a range fromabout 30% to about 70% by weight of total solids within the starch-boundcellular matrix.
 22. An article of manufacture as defined in claim 1,wherein the inorganic aggregate is included in an amount in a range fromabout 40% to about 60% by weight of total solids within the starch-boundcellular matrix.
 23. An article of manufacture as defined in claim 1,wherein the article has a specific heat in a range from about 0.1 J/g·Kto about 400 J/g·K at 20° C.
 24. An article of manufacture as defined inclaim 1, wherein the article has a specific heat in a range betweenabout 0.15 J/g·K to about 50 J/g·K at 20° C.
 25. An article ofmanufacture as defined in claim 1, wherein the article has a specificheat in a range between about 0.2 J/g·K to about 20 J/g·K at 20° C. 26.An article of manufacture as defined in claim 1, wherein thestarch-bound cellular matrix further includes a mold-releasing agent.27. An article of manufacture as defined in claim 26, wherein themold-releasing agent includes a fatty acid having a carbon chain greaterthan about C₁₂.
 28. An article of manufacture as defined in claim 26,wherein the mold-releasing agent includes a salt of a fatty acid.
 29. Anarticle of manufacture as defined in claim 26, wherein themold-releasing agent includes an acid derivative of a fatty acid.
 30. Anarticle of manufacture as defined in claim 26, wherein themold-releasing agent includes magnesium stearate.
 31. An article ofmanufacture as defined in claim 26, wherein the mold-releasing agentincludes a wax.
 32. An article of manufacture as defined in claim 26,wherein the mold-releasing agent is included in an amount in a rangefrom about 0.5% to about 10% by weight of total solids within thestarch-bound cellular matrix.
 33. An article of manufacture as definedin claim 1, wherein the starch-bound cellular matrix further includesfibers dispersed therein.
 34. An article of manufacture as defined inclaim 33, wherein the fibers are included in an amount in a range fromabout 0.5% to about 60% by volume of solids within the starch-boundcellular matrix.
 35. An article of manufacture as defined in claim 33,wherein the fibers are included in an amount in a range from about 2% toabout 40% by volume of solids within the starch-bound cellular matrix.36. An article of manufacture as defined in claim 33, wherein the fibersare included in an amount in a range from about 5% to about 20% byvolume of solids within the starch-bound cellular matrix.
 37. An articleof manufacture as defined in claim 33, wherein the fibers includes sisalfibers.
 38. An article of manufacture as defined in claim 33, whereinthe fibers are selected from the group consisting of fibers derived fromhemp, cotton, plant, leaves, abaca, bagasse, wood, and mixtures thereof.39. An article of manufacture as defined in claim 33, wherein the fibersare selected from the group of fibers consisting of glass, graphite,silica, ceramic, metals, and mixtures thereof.
 40. An article ofmanufacture as defined in claim 33, wherein the fibers have an averagediameter in a range from about 10 μm to about 100 μm.
 41. An article ofmanufacture as defined in claim 33, wherein the fibers have an averagediameter in a range from about 50 μm to about 100 μm.
 42. An article ofmanufacture as defined in claim 1, wherein the starch-bound cellularmatrix further includes a rheology-modifying agent.
 43. An article ofmanufacture as defined in claim 42, wherein the rheology-modifying agentincludes a cellulose-based material.
 44. An article of manufacture asdefined in claim 43, wherein the cellulose-based material is selectedfrom the group consisting of methylhydroxyethylcellulose,hydroxymethylcellulose, carboxymethylcellulose, methylcellulose,ethylcellulose, hydroxyethylcellulose, hydroxyethylpropylcellulose,hydroxypropylmethylcellulose, and mixtures or derivatives thereof. 45.An article of manufacture as defined in claim 42, wherein therheology-modifying agent includes a polysaccharide-based material. 46.An article of manufacture as defined in claim 45, wherein thepolysaccharide-based material is selected from the group consisting ofalginic acid, phycocolloids, agar, gum arabic, guar gum, locust beangum, gum karaya, gum tragacanth, and mixtures or derivatives thereof.47. An article of manufacture as defined in claim 42, wherein therheology-modifying agent includes a protein-based material.
 48. Anarticle of manufacture as defined in claim 47, wherein the protein-basedmaterial is selected from a group consisting of prolamine, collagen,casein, and mixtures or derivatives thereof.
 49. An article ofmanufacture as defined in claim 42, wherein the rheology-modifying agentincludes a synthetic organic material.
 50. An article of manufacture asdefined in claim 49, wherein the synthetic organic material is selectedfrom the group consisting of polyethylene glycol, polyvinyl alcohol,polyvinyl acetate, polyacrylic acids, polylactic acid, and mixtures orderivatives thereof.
 51. An article of manufacture as defined in claim42, wherein the rheology-modifying agent is included in an mount in arange from about 0.5% to about 10% by weight of total solids within thestarch-bound cellular matrix.
 52. An article of manufacture as definedin claim 1, wherein the starch-bound cellular matrix further includes adispersant.
 53. An article of manufacture as defined in claim 52,wherein the dispersant is selected from the group consisting ofsulphonated melamine-formaldehyde condensate, lignosulfonate, andpolyacrylic acid.
 54. An article of manufacture as defined in claim 1,wherein the starch-bound cellular matrix further includes an enzyme. 55.An article of manufacture as defined in claim 54, wherein the enzyme isselected from the group consisting of carbohydrases, amylase, oxidase,and mixtures or derivatives thereof.
 56. An article of manufacture asdefined in claim 54, wherein the enzyme is included in an amount in arange from about 0.5% to about 10% by weight of total solids within thestarch-bound cellular matrix.
 57. An article of manufacture as definedin claim 1, wherein the starch-bound cellular matrix further includes ahumectant for maintaining moisture within the cellular matrix andincreasing the flexibility of the article.
 58. An article of manufactureas defined in claim 57, wherein the humectant is selected from the groupconsisting of MgCl₂, CaCl₂, NaCl, calcium citrate, and mixtures thereof.59. An article of manufacture as defined in claim 1, wherein thestarch-bound cellular matrix includes a cross-linking material.
 60. Anarticle of manufacture as defined in claim 59, wherein the cross-linkingmaterial is selected from the group consisting of dialdehydes,methylureas, melamine formaldehyde resins, and mixtures or derivativesthereof.
 61. An article of manufacture as defined in claim 59, whereinthe cross-linking material is included in an amount in a range fromabout 0.5% to about 5% by weight of total solids within the starch-boundcellular matrix.
 62. An article of manufacture as defined in claim 1,wherein the starch-bound cellular matrix has a density in a range fromabout 0.05 g/cm³ to about 1 g/cm³.
 63. An article of manufacture asdefined in claim 1, wherein the starch-bound cellular matrix has adensity in a range from about 0.1 g/cm³ to about 0.5 g/cm³.
 64. Anarticle of manufacture as defined in claim 1, wherein the articlecomprises a container.
 65. An article of manufacture as defined in claim64, wherein the container is a cup.
 66. An article of manufacture asdefined in claim 64, wherein the container is a plate.
 67. An article ofmanufacture as defined in claim 64, wherein the container is aclam-shell.
 68. An article of manufacture as defined in claim 1, whereinthe starch-bound cellular matrix has a thickness in a range from about0.5 mm to about 6 mm.
 69. An article of manufacture as defined in claim1, wherein the starch-bound cellular matrix has a thickness in a rangefrom about 1 mm to about 3 mm.
 70. An article of manufacture as definedin claim 1, wherein the starch-bound cellular matrix further includes acoating on at least a portion of a surface thereof.
 71. An article ofmanufacture as defined in claim 70, wherein the coating includes a wax.72. An article of manufacture as defined in claim 1, wherein thestarch-bound cellular matrix further includes a plasticizer that impartsflexibility to the article.
 73. An article of manufacture as defined inclaim 72, wherein the plasticizer comprises glycerin.
 74. An article ofmanufacture as defined in claim 72, wherein the plasticizer is selectedfrom the group consisting of monoglycerides, diglycerides, polyethyleneglycol, sorbitol, and mixtures or derivatives thereof.
 75. An article ofmanufacture as defined in claim 1, wherein the inorganic aggregateincludes a porous inorganic aggregate capable of absorbing water duringmolding of the article and thereafter releasing the water into thestarch-bound cellular matrix after the article has been molded.
 76. Anarticle of manufacture as defined in claim 1, wherein the article has athermal resistance in a range from about 0.04 W/m·K to about 0.2 W/m·K.77. An article of manufacture as defined in claim 1, wherein the articlehas a thermal resistance in a range from about 0.04 W/m·K to about 0.06W/m·K.
 78. An article of manufacture as defined in claim 1, wherein thestarch-bound cellular matrix further includes an inert organicaggregate.
 79. An article of manufacture as defined in claim 78, whereinthe inert organic aggregate is selected from the group consisting ofseeds, grains, cork, plastic spheres, and mixtures thereof.
 80. Anarticle of manufacture as defined in claim 78, wherein the inert organicaggregate is included in an amount in a range from about 5% to about 60%by weight of total solids in starch-bound cellular matrix.
 81. Anarticle of manufacture as defined in claim 78, wherein the inert organicaggregate is included in an amount in a range from about 15% to about50% by weight of total solids in the starch-bound cellular matrix. 82.An article of manufacture as defined in claim 78, wherein the inertorganic aggregate is included in an amount in a range from about 25% toabout 40% by weight of total solids in the starch-bound cellular matrix.83. An article of manufacture comprising a starch-bound cellular matrixof starch and inorganic aggregate reinforced with fibers, thestarch-bound cellular matrix comprising:a starch-based binder that hasbeen substantially gelatinized by water and then hardened through theremoval of a substantial quantity of the water by evaporation; aninorganic aggregate dispersed throughout the starch-bound cellularmatrix and included in an amount in a range from about 20% to about 90%by weight of solids within the starch-bound cellular matrix; and fibersdispersed throughout the starch-bound cellular matrix and included in anamount in a range from about 2% to about 40% by volume of solids withinthe starch-bound cellular matrix,wherein the starch-bound cellularmatrix has a thickness less than about 6 mm and degrades after prolongedexposure to water.
 84. An article of manufacture as defined in claim 83,further including a coating on at least a portion of the article.
 85. Anarticle of manufacture as defined in claim 83, wherein the starch-boundcellular matrix further includes glycerin.
 86. An article of manufactureas defined in claim 83, wherein the starch-bound cellular matrix furtherincludes a material selected from the group consisting of polyethyleneglycol, polyvinyl alcohol, polyvinyl acetate, polyacrylic acids,polylactic acid, sorbitol, and mixtures or derivatives thereof.
 87. Anarticle of manufacture as defined in claim 83, wherein the starch-basedbinder includes a potato starch.
 88. An article of manufacture asdefined in claim 83, wherein the starch-based binder includes a modifiedstarch.
 89. An article of manufacture as defined in claim 83, whereinthe starch-based binder is included in an amount in a range from about10% to about 80% by weight of total solids within the starch-boundcellular matrix.
 90. An article of manufacture as defined in claim 83,wherein the starch-based binder is included in an amount in a range fromabout 30% to about 70% by weight of total solids within the starch-boundcellular matrix.
 91. An article of manufacture as defined in claim 83,wherein the starch-based binder is included in an amount in a range fromabout 40% to about 60% by weight of total solids within the starch-boundcellular matrix.
 92. An article of manufacture as defined in claim 83,wherein the inorganic aggregate includes calcium carbonate.
 93. Anarticle of manufacture as defined in claim 83, wherein the inorganicaggregate includes sand.
 94. An article of manufacture as defined inclaim 83, wherein the inorganic aggregate is included in an amount in arange from about 30% to about 70% by weight of total solids within thestarch-bound cellular matrix.
 95. An article of manufacture as definedin claim 83, wherein the inorganic aggregate is included in an amount ina range from about 40% to about 60% by weight of total solids within thestarch-bound cellular matrix.
 96. An article of manufacture as definedin claim 83, wherein the starch-bound cellular matrix further includes amold-releasing agent.
 97. An article of manufacture as defined in claim94, wherein the mold-releasing agent includes magnesium stearate.
 98. Anarticle of manufacture as defined in claim 83, wherein said fibers aresubstantially homogeneously dispersed.
 99. An article of manufacture asdefined in claim 83, wherein the fibers are included in an amount in arange from about 0.5% to about 60% by volume of solids within thestarch-bound cellular matrix.
 100. An article of manufacture as definedin claim 83, wherein the fibers are included in an amount in a rangefrom about 2% to about 40% by volume of solids within the starch-boundcellular matrix.
 101. An article of manufacture as defined in claim 83,wherein the fibers are included in an amount in a range from about 5% toabout 20% by volume of solids within the starch-bound cellular matrix.102. An article of manufacture as defined in claim 83, wherein thefibers are selected from the group consisting of fibers derived fromsisal, hemp, cotton, plant, leaves, abaca, bagasse, wood, and mixturesthereof.
 103. An article of manufacture as defined in claim 83, whereinthe fibers are selected from the group of fibers consisting of glass,graphite, silica, ceramic, metals, and mixtures thereof.
 104. An articleof manufacture as defined in claim 83, wherein the starch-bound cellularmatrix further includes a material selected from the group consisting ofalginic acid, phycocolloids, agar, gum arabic, guar gum, locust beangum, gum karaya, gum tragacanth, and mixtures or derivatives thereof.105. An article of manufacture as defined in claim 83, wherein thestarch-bound cellular matrix further includes a material selected from agroup consisting of prolamine, collagen, casein, and mixtures orderivatives thereof.
 106. An article of manufacture as defined in claim83, wherein the starch-bound cellular matrix further includes a materialselected from the group consisting of polyethylene glycol, polyvinylalcohol, polyvinyl acetate, polyacrylic acids, polylactic acid, andmixtures or derivatives thereof.
 107. An article of manufacture asdefined in claim 83, wherein the starch-bound cellular matrix has adensity in a range from about 0.05 g/cm³ to about 1 g/cm³.
 108. Anarticle of manufacture as defined in claim 83, wherein the starch-boundcellular matrix has a density in a range from about 0.1 g/cm³ to about0.5 g/cm³.
 109. An article of manufacture as defined in claim 83,wherein the article comprises a container.
 110. An article ofmanufacture as defined in claim 109, wherein the container is a cup.111. An article of manufacture as defined in claim 109, wherein thecontainer is a plate.
 112. An article of manufacture as defined in claim109, wherein the container is a clam-shell.
 113. An article ofmanufacture as defined in claim 83, wherein the starch-bound cellularmatrix has a thickness in a range from about 1 mm to about 3 mm.
 114. Anarticle of manufacture as defined in claim 84, wherein the coatingincludes a wax.
 115. An article of manufacture comprising a starch-boundcellular matrix of starch and inorganic aggregate reinforced withfibers, the starch-bound cellular matrix comprising:a starch binderselected from the group consisting of potato starch, corn starch, andwaxy corn starch, the starch binder having been substantiallygelatinized by water and then hardened through the removal of asubstantial quantity of the water by evaporation, the starch binderhaving a concentration in a range from about 30% to about 70% by weightof solids within the starch-bound cellular matrix; an inorganicaggregate dispersed throughout the starch-bound cellular matrix andincluded in an amount in a range from about 30% to about 70% by weightof solids within the starch-bound cellular matrix; and organic fibersdispersed throughout the starch-bound cellular matrix and included in anamount up to about 20% by volume of solids within the starch-boundcellular matrix,wherein the starch-bound cellular matrix has a thicknessless than about 6 mm and degrades after prolonged exposure to water.116. An article of manufacture as defined in claim 115, furtherincluding a coating on at least a portion of the article.
 117. Anarticle of manufacture as defined in claim 115, wherein the starch-boundcellular matrix farther includes glycerin.
 118. An article ofmanufacture as defined in claim 115, wherein the starch-bound cellularmatrix further includes a material selected from the group consisting ofpolyethylene glycol, polyvinyl alcohol, polyvinyl acetate, polyacrylicacids, polylactic acid, sorbitol, and mixtures or derivatives thereof.119. An article of manufacture as defined in claim 115, wherein thestarch-based binder includes a modified starch.
 120. An article ofmanufacture as defined in claim 115, wherein the starch-based binder isincluded in an amount in a range from about 40% to about 60% by weightof total solids within the starch-bound cellular matrix.
 121. An articleof manufacture as defined in claim 115, wherein the inorganic aggregateincludes calcium carbonate.
 122. An article of manufacture as defined inclaim 115, wherein the inorganic aggregate includes sand.
 123. Anarticle of manufacture as defined in claim 115, wherein the inorganicaggregate is included in an amount in a range from about 40% to about60% by weight of total solids within the starch-bound cellular matrix.124. An article of manufacture as defined in claim 115, wherein thestarch-bound cellular matrix further includes a mold-releasing agent.125. An article of manufacture as defined in claim 124, wherein themold-releasing agent includes magnesium stearate.
 126. An article ofmanufacture as defined in claim 115, wherein the fibers are selectedfrom the group consisting of fibers derived from sisal, hemp, cotton,plant, leaves, abaca, bagasse, wood, and mixtures thereof.
 127. Anarticle of manufacture as defined in claim 115, wherein the fibers areselected from the group of fibers consisting of glass, graphite, silica,ceramic, metals, and mixtures thereof.
 128. An article of manufacture asdefined in claim 115, wherein the starch-bound cellular matrix furtherincludes a material selected from the group consisting of alginic acid,phycocolloids, agar, gum arabic, guar gum, locust bean gum, gum karaya,gum tragacanth, and mixtures or derivatives thereof.
 129. An article ofmanufacture as defined in claim 115, wherein the starch-bound cellularmatrix further includes a material selected from a group consisting ofprolamine, collagen, casein, and mixtures or derivatives thereof. 130.An article of manufacture as defined in claim 115, wherein thestarch-bound cellular matrix further includes a material selected fromthe group consisting of polyethylene glycol, polyvinyl alcohol,polyvinyl acetate, polyacrylic acids, polylactic acid, and mixtures orderivatives thereof.
 131. An article of manufacture as defined in claim115, wherein the starch-bound cellular matrix has a density in a rangefrom about 0.05 g/cm³ to about 1 g/cm³.
 132. An article of manufactureas defined in claim 115, wherein the starch-bound cellular matrix has adensity in a range from about 0.1 g/cm³ to about 0.5 g/cm³.
 133. Anarticle of manufacture as defined in claim 115, wherein the articlecomprises a container.
 134. An article of manufacture as defined inclaim 133, wherein the container is a cup.
 135. An article ofmanufacture as defined in claim 133, wherein the container is a plate.136. An article of manufacture as defined in claim 133, wherein thecontainer is a clam-shell.
 137. An article of manufacture as defined inclaim 115, wherein the starch-bound cellular matrix has a thickness in arange from about 1 mm to about 3 mm.
 138. An article of manufacture asdefined in claim 116, wherein the coating includes a wax.
 139. Anarticle of manufacture comprising a starch-bound cellular matrix ofstarch and inorganic aggregate, the starch-bound cellular matrixcomprising:a starch-based binder that has been substantially gelatinizedby water and then hardened through the removal of a substantial quantityof the water by evaporation; and an inorganic aggregate dispersedthroughout the starch-bound cellular matrix in a concentration in arange from about 20% to about 90% by weight of total solids within thestarch-bound cellular matrix,wherein the starch-bound cellular matrixhas a thickness less than about 1 cm and degrades after prolongedexposure to water, wherein the article includes a coating on at least aportion thereof.
 140. An article of manufacture as defined in claim 139,wherein the starch-based binder includes a potato starch.
 141. Anarticle of manufacture as defined in claim 139, wherein the starch-basedbinder includes a modified starch.
 142. An article of manufacture asdefined in claim 139, wherein the inorganic aggregate includes calciumcarbonate.
 143. An article of manufacture as defined in claim 139,wherein the inorganic aggregate is included in an amount in a range fromabout 30% to about 70% by weight of total solids within the starch-boundcellular matrix.
 144. An article of manufacture as defined in claim 139,wherein the inorganic aggregate is included in an amount in a range fromabout 40% to about 60% by weight of total solids within the starch-boundcellular matrix.
 145. An article of manufacture as defined in claim 139,wherein the fibers are selected from the group consisting of fibersderived from sisal, hemp, cotton, plant, leaves, abaca, bagasse, wood,and mixtures thereof.
 146. An article of manufacture as defined in claim139, wherein the starch-bound cellular matrix further includes amaterial selected from the group consisting of alginic acid,phycocolloids, agar, gum arabic, guar gum, locust bean gum, gum karaya,gum tragacanth, and mixtures or derivatives thereof.
 147. An article ofmanufacture as defined in claim 139, wherein the starch-bound cellularmatrix has a thickness in a range from about 1 mm to about 3 mm.
 148. Anarticle of manufacture as defined in claim 139, wherein the coatingincludes a wax.
 149. An article of manufacture as defined in claim 139,wherein the starch-bound cellular matrix further includes glycerinwithin a portion thereof.
 150. An article of manufacture comprising astarch-bound cellular matrix of starch and inorganic aggregatereinforced with fibers, the starch-bound cellular matrix comprising:astarch-based binder that has been substantially gelatinized by water andthen hardened through the removal of a substantial quantity of the waterby evaporation; an inorganic aggregate dispersed throughout thestarch-bound cellular matrix and included in an amount in a range fromabout 20% to about 90% by weight of solids within the starch-boundcellular matrix; and fibers dispersed throughout the starch-boundcellular matrix and included in an amount in a range from about 2% toabout 40% by volume of solids within the starch-bound cellularmatrix,wherein the starch-bound cellular matrix has a thickness lessthan about 6 mm, includes glycerin within a portion thereof, anddegrades after prolonged exposure to water.
 151. An article ofmanufacture as defined in claim 150, wherein the starch-bound cellularmatrix further includes a coating material on at least a portionthereof.
 152. An article of manufacture as defined in claim 151, whereinthe coating includes a wax.
 153. An article of manufacture as defined inclaim 150, wherein the inorganic aggregate includes calcium carbonate.154. An article of manufacture comprising a starch-bound cellular matrixof starch and inorganic aggregate reinforced with fibers, thestarch-bound cellular matrix comprising:a starch binder selected fromthe group consisting of potato starch, corn starch, and waxy cornstarch, the starch binder having been substantially gelatinized by waterand then hardened through the removal of a substantial quantity of thewater by evaporation, the starch binder having a concentration in arange from about 30% to about 70% by weight of solids within thestarch-bound cellular matrix; calcium carbonate dispersed throughout thestarch-bound cellular matrix and included in an amount in a range fromabout 30% to about 70% by weight of solids within the starch-boundcellular matrix; and organic fibers dispersed throughout thestarch-bound cellular matrix and included in an amount up to about 20%by volume of solids within the starch-bound cellular matrix,wherein thestarch-bound cellular matrix has a thickness less than about 6 mm anddegrades after prolonged exposure to water, wherein the article includesa coating on at least a portion thereof.
 155. An article of manufactureas defined in claim 154, wherein the starch-bound cellular matrixfurther includes glycerin within a portion thereof.
 156. An article ofmanufacture as defined in claim 154, wherein the coating includes a wax.157. An article of manufacture as defined in claim 154, wherein thestarch-bound cellular matrix has a thickness less than about 3 mm.